SQUISH: add test to check for unnecessary broadcast traffic

It should be possible to test for an incorrect address list setting that sends EPICS broadcast traffic to the private network. This test would need to happen on a system running IOCs, client, python (both in gui and outside). Maybe a separate test in squish, or maybe just a background process and a nagios monitor on the squish server so it looks for any broadcasts across everything.

A python program to listen for EPICS broadcasts is needed, but should be quite simple - it just needs to bind to the private interface and listen for any UDP traffic going to ports 5064 and 5065 and then e.g. increment a counter that can be queried