Use milter framework to handle libmilter correctly
updated pkg-plist to use @sample, and changed SMF_RUN_DIR to be substituted
in the plist otherwise packaging will fail it it's redefined.
Bumped PORTREVISION.

PR: 214722
Submitted by: sasaki@fcc.ad.jp (maintainer)
Approved by: adamw (mentor)
Differential Revision: https://reviews.freebsd.org/D9126