Possible workaround for NAT problems

[szaimen]

From #4519

Situation:

I have two VMs in my setup. One is hosting AIO.
One is hosting router, NAT, and RP.

When setting up AIO (in RP mode), the network check always failed. After analysis, I discovered that:

from internet, I can access NC components check (signaling-standalone/api/v1/welcome for Talk, or /hosting/discovery for Collabora)
from inside a container, I could never curl these URLs. Network failure.

Solution

There is some configuration to do on the NAT side to allow port forwarding back onto the same network. See:
https://www.netfilter.org/documentation/HOWTO/NAT-HOWTO-10.html