pfctl: robustness improvement on address family

The kernel does not set the address family for the socket addresses
that are used for netmask, broadcast, and destination address. In
pfctl(8) take the family of the interface address and write it to
the other addresses. This fixes some bugs when copy_satopfaddr()
copied only part of IPv6 addresses. Print a warning if the address
family is unknown.
OK kn@

Obtained from: OpenBSD, bluhm <bluhm@openbsd.org>, 1fef2296ff
Sponsored by: Rubicon Communications, LLC ("Netgate")