pf: merge pf_scrub_ip() and pf_scrub_ip6()

[kp]

Summary

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 <[e-mail]>, 48c45e6969
Sponsored by: Rubicon Communications, LLC ("Netgate")

[zlei]

sys/netpfil/pf/pf_norm.c

2281–2283

Emm, I'd personally prefer big switch case blocks, rather than test pd->af everywhere. But no objection since it is from upstream.