Mock network interfaces in `systems.json`

[thanasipantazides]

Why

It would be very handy to be able to test the Formatter network interfaces without anything actually plugged in (no SPMU-001/no GSE). We can approximate this with loopback testing.

To do

• [x] Choose two port numbers: one for TCP traffic with SPMU-001, and one for UDP traffic with GSE.
• [x] Write a test version of foxsi4-commands/systems.json where:
  • [x] you replace the ethernet_interface in gse to use the loopback IP (127.0.0.1) and your chosen UDP port number
  • [x] you replace the ethernet_interface in cdtede, cdte1, cdte2, cdte3, cdte4, cmos1, and cmos2 with the loopback IP (127.0.0.1) and your chose TCP port number

This will give the Formatter software something to connect to, and not error out on startup. Next, we could write a Python script to sit on the Formatter and send some fake data out when it receives certain loopback packets.

[thanasipantazides]

This is done. See foxsi4-commands/foxsimile_systems.json and the local Foxsimile.h/Foxsimile.cpp files.

This testing framework still needs documentation, but the essentials are done. See #49 for remaining work on this topic.