Add ipfilter support to blacklistd-helper

In addition to adding initial support for the ipfilter
packet filtering system, wrap a few long lines, perform
whitespace cleanup and sync with upstream changes made
in NetBSD.

Submitted by: cy
Reviewed by: cy
Approved by: re (hrs)
Relnotes: YES
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D6823