pf: merge pf_test() and pf_test6()
Bye bye pf_test6(). Only one pf_test function for both IPv4 and v6.
The functions were 95% identical anyway.
OK bluhm@ mcbride@ and most probably henning@ as well
Obtained from: OpenBSD, claudio <claudio@openbsd.org>, c8bc4f6e29
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D46649