Automatically configure DNS64 when forwarding is enabled for IPV4ONLY.ARPA

When the IPV4ONLY.ARPA namespace is covered by a forward directive periodically query for IPV4ONLY.ARPA/AAAA using that forward directive and if AAAA records are found, construct DNS64 prefixes based on the returned addresses. See RFC 7050.

Additionally look for IPV4ONLY.ARPA/APL for exclusion acls. Family 1 for mapped and family 2 for excluded. If not found populate mapped with RFC 1918 addresses and populate excluded with ::ffff:0:0/96 as per RFC 6174.