sgwu cannot bind 0.0.0.0

[spencersevilla]

Default open5gs has sgwu binding some localhost value. For it to receive conns from outside eNBs it needs to bind something else. 0.0.0.0 would be best but it interfers with upf binding localhost on port 2123.

One approach is for sgwu to magically know the correct IP address it's listening on. Far better approach is to use a custom port for upf, like 2124. This way sgwu can listen to everyone and we no longer need any super network specific custom vals.