pf: merge pf_scrub_ip() and pf_scrub_ip6()

Merge pf_scrub_ip() and pf_scrub_ip6() into a single function. Call
pf_scrub with the right arugments in the rule case so that match
rules will work as expected.

OK henning@

Obtained from: OpenBSD, claudio <claudio@openbsd.org>, 48c45e6969
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D46597