Make address family search via UDP socket hack more accurate

The following address family search functions don't always return an IPv6 address:

• get_interface_address6_via_udp_socket_hack takes an address family as its first argument
  • when get_interface_address6_list is passed AF_UNSPEC, it should be call get_interface_address6_via_udp_socket_hack with AF_INET, and then AF_INET6, and then both addresses should be returned