Address families: inet vs inet6

We support IPv4 and IPv6 address families, dual stack systems can filter on both

inet denotes IPv4 traffic

inet6 denotes IPv6 traffic

    pass inet proto tcp port $ipv4services from $ipv4clients
    pass inet6 proto tcp port $ipv6services from $ipv6clients

(add appropriate macro definitions)

Note: on dual-stack systems, rules with no address family specified will match both AFs

In OpenBSD 5.1 onwards, we have NAT64 via af-to