net/af_xdp: enable uds_path instead of use_cni

With the original 'use_cni' implementation, (using a
hardcoded socket rather than a configurable one),
if a DPDK pod is requesting multiple net devices
and these devices are from different pools, then
the container attempts to mount all the netdev UDSes
in the pod as /tmp/afxdp.sock. Which means that at best
only 1 netdev will handshake correctly with the AF_XDP
DP. This patch addresses this by making the socket
parameter configurable using a new vdev param called
'uds_path' and removing the previous 'use_cni' param.
This patch also fixes incorrect references to the
AF_XDP DP as CNI and updates the documentation with a
working example. This change has been tested with the
AF_XDP DP PR 81[1], with both single and multiple interfaces.

[1] intel/afxdp-plugins-for-kubernetes#81

v6:
* Add link to PR 81 in commit message
* Add release notes changes to this patchset

v5:
* Fix alignment for ETH_AF_XDP_USE_DP_UDS_PATH_ARG
* Remove use_cni references in af_xdp.rst

v4:
* Rename af_xdp_cni.rst to af_xdp_dp.rst
* Removed all incorrect references to CNI throughout af_xdp
  PMD file.
* Fixed Typos in af_xdp_dp.rst

v3:
* Remove `use_cni` vdev argument as it's no longer needed.
* Update incorrect CNI references for the AF_XDP DP in the
  documentation.
* Update the documentation to run a simple example with the
  AF_XDP DP plugin in K8s.

v2:
* Rename sock_path to uds_path.
* Update documentation to reflect when CAP_BPF is needed.
* Fix testpmd arguments in the provided example for Pods.
* Use AF_XDP API to update the xskmap entry.

Signed-off-by: Maryam Tahhan <mtahhan@redhat.com>
Reviewed-by: Ciara Loftus <ciara.loftus@intel.com>
Signed-off-by: 0-day Robot <robot@bytheb.org>