Fixes AMQP Credits handling in vanflow/session

[c-kruse]

Sets the configured credits on the vanflow receiver. Before it was mistakenly only setting credits when they were negative instead of when positive.

[c-kruse]

Example skstat -l output: note the final cred column.

[christian@rh skupper] (bugfix-vanflow-credits)$ k exec -it deployments/skupper-router -c router -- skstat -l
...
Router Links
  type            dir  conn id  id   class   addr                                                    cap  pri  undel  unsett  deliv  presett  psdrop  acc    rej  rel  mod  delay  rate  stuck  cred  blkd
  ==========================================================================================================================================================================================================
  ...
# Links for v2-latest network-observer
  endpoint        out  10       69   mobile  mc/sfe.all                                              250  4    0      0       20018  10008    0       10010  0    0    0    0      0     0      1     -
  endpoint        out  11       70   mobile  mc/sfe.73e06170-6bc7-4ac2-bf9a-c0a3ce8b8b5e             250  4    0      0       13     0        0       13     0    0    0    0      0     0      1     -
  endpoint        out  11       71   mobile  mc/sfe.73e06170-6bc7-4ac2-bf9a-c0a3ce8b8b5e.heartbeats  250  4    0      0       16684  0        0       16684  0    0    0    0      0     0      1     -
  endpoint        in   11       72   mobile  sfe.73e06170-6bc7-4ac2-bf9a-c0a3ce8b8b5e                250  4    0      0       1      0        0       1      0    0    0    0      0     0      250   -
  endpoint        out  11       73   mobile  mc/sfe.9a5a7588-d3a0-46af-bbf2-399e219acd10             250  4    0      0       13     0        0       13     0    0    0    0      0     0      1     -
  endpoint        out  11       74   mobile  mc/sfe.9a5a7588-d3a0-46af-bbf2-399e219acd10.heartbeats  250  4    0      0       16684  0        0       16684  0    0    0    0      0     0      1     -
  endpoint        in   11       75   mobile  sfe.9a5a7588-d3a0-46af-bbf2-399e219acd10                250  4    0      0       1      0        0       1      0    0    0    0      0     0      250   -
  endpoint        out  11       76   mobile  mc/sfe.82tft:0                                          250  4    0      0       50010  50010    0       0      0    0    0    0      1     0      1     -
  endpoint        out  11       77   mobile  mc/sfe.82tft:0.flows                                    250  4    0      0       0      0        0       0      0    0    0    0      0     0      1     -
  endpoint        out  11       78   mobile  mc/sfe.572gf:0                                          250  4    0      0       50011  50011    0       0      0    0    0    0      1     0      1     -
  endpoint        out  11       79   mobile  mc/sfe.572gf:0.flows                                    250  4    0      0       24665  24665    0       0      0    0    0    0      1     0      1     -
  endpoint        out  11       80   mobile  mc/sfe.rj7jn:0.flows                                    250  4    0      0       30941  30941    0       0      0    0    0    0      1     0      1     -
  endpoint        out  11       81   mobile  mc/sfe.rj7jn:0                                          250  4    0      0       16687  16687    0       0      0    0    0    0      0     0      1     -
  endpoint        in   11       82   mobile  sfe.572gf:0                                             250  4    0      0       1      0        0       1      0    0    0    0      0     0      250   -
  endpoint        in   11       83   mobile  sfe.82tft:0                                             250  4    0      0       1      0        0       1      0    0    0    0      0     0      250   -
  endpoint        out  11       84   mobile  mc/sfe.278e3426-b1ef-4a78-89d8-5b19a918cd82             250  4    0      0       8      0        0       8      0    0    0    0      0     0      1     -
  endpoint        out  11       85   mobile  mc/sfe.278e3426-b1ef-4a78-89d8-5b19a918cd82.heartbeats  250  4    0      0       16680  0        0       16680  0    0    0    0      0     0      1     -
  endpoint        in   11       86   mobile  sfe.278e3426-b1ef-4a78-89d8-5b19a918cd82                250  4    0      0       1      0        0       1      0    0    0    0      0     0      250   -
  endpoint        in   11       87   mobile  sfe.rj7jn:0                                             250  4    0      0       1      0        0       1      0    0    0    0      0     0      250   -
...
# Links for network-observer with patched vanflow/session
  endpoint        out  37       163  mobile  mc/sfe.all                                              250  4    0      0       5      3        0       2      0    0    0    0      0     0      1     -
  endpoint        out  38       164  mobile  mc/sfe.82tft:0                                          250  4    0      0       10     10       0       0      0    0    0    0      1     0      246   -
  endpoint        out  38       165  mobile  mc/sfe.82tft:0.flows                                    250  4    0      0       0      0        0       0      0    0    0    0      0     0      256   -
  endpoint        out  38       166  mobile  mc/sfe.73e06170-6bc7-4ac2-bf9a-c0a3ce8b8b5e.heartbeats  250  4    0      0       4      0        0       4      0    0    0    0      0     0      252   -
  endpoint        out  38       167  mobile  mc/sfe.73e06170-6bc7-4ac2-bf9a-c0a3ce8b8b5e             250  4    0      0       2      0        0       2      0    0    0    0      0     0      254   -
  endpoint        out  38       168  mobile  mc/sfe.9a5a7588-d3a0-46af-bbf2-399e219acd10.heartbeats  250  4    0      0       4      0        0       4      0    0    0    0      0     0      252   -
  endpoint        out  38       169  mobile  mc/sfe.9a5a7588-d3a0-46af-bbf2-399e219acd10             250  4    0      0       2      0        0       2      0    0    0    0      0     0      254   -
  endpoint        in   38       170  mobile  sfe.73e06170-6bc7-4ac2-bf9a-c0a3ce8b8b5e                250  4    0      0       1      0        0       1      0    0    0    0      0     0      250   -
  endpoint        in   38       171  mobile  sfe.9a5a7588-d3a0-46af-bbf2-399e219acd10                250  4    0      0       1      0        0       1      0    0    0    0      0     0      250   -
  endpoint        out  38       172  mobile  mc/sfe.572gf:0                                          250  4    0      0       10     10       0       0      0    0    0    0      1     0      246   -
  endpoint        out  38       173  mobile  mc/sfe.572gf:0.flows                                    250  4    0      0       7      7        0       0      0    0    0    0      1     0      249   -
  endpoint        out  38       174  mobile  mc/sfe.rj7jn:0                                          250  4    0      0       4      4        0       0      0    0    0    0      0     0      252   -
  endpoint        out  38       175  mobile  mc/sfe.rj7jn:0.flows                                    250  4    0      0       8      8        0       0      0    0    0    0      1     0      248   -
  endpoint        in   38       176  mobile  sfe.82tft:0                                             250  4    0      0       1      0        0       1      0    0    0    0      0     0      250   -
  endpoint        in   38       177  mobile  sfe.572gf:0                                             250  4    0      0       1      0        0       1      0    0    0    0      0     0      250   -
  endpoint        in   38       178  mobile  sfe.rj7jn:0                                             250  4    0      0       1      0        0       1      0    0    0    0      0     0      250   -
...