Allow null TARGET_IP - Waits for first keepalive to update - use for
endpoints that are on a dynamic or unknown IP

Support IPv6 for OBP - to listen IPv6 set IP: :: or other valid ipv6 address

IPv6 addresses can be used in TARGET_IP or will be resolved from DNS

Note, might cause confusion if the target has an IPv6 address and we don't
take note of this and specify ipv4 explicitly if needs be.

IPv6 Needs some testing :-)