mail/opendkim: Respect PidFile setting in opendkim.conf

While here, pet rclint a bit, though it doesn't like the profile parts
not being in functions

PR: ports/254762
Reported by: Rob LA LAU <freebsd@ohreally.nl>
Reviewed by: skozlov (a previous iteration)
Approved by: maintainer timeout, 9 months
Differential Revision: https://reviews.freebsd.org/D29586