Determines if the given IP address is a private address, i.e. not routable on the public internet.
These are the ranges: 127.0.0.1, 10.0.0.0-10.255.255.255, 172.16.0.0-172.31.255.255, 192.168.0.0-192.168.255.255.
If so, allow MQTT publication the same as existing localhost support.
