Test fix for #4306
Test fix for #4305
Configurable fix for #4305

Rename UDP_SECRET to just SECRET, as it is used for more than just UDP

Rename and properly document GATEWAY option

Introduce an option to configure what UDP port will be probed
Update any modules that deregistered NETMASK
Merge branch '4306' into 4305
Update GATEWAY to GATEWAY_PROBE_HOST, add GATEWAY_PROBE_PORT
Add missing opt ,
Correctly set default SECRET
Land #4317 and #4306, fix netmask tomfoolery