Most of daemons like bgpd, ospfd, smtpd, relayd, ... use to return
"configuration OK" when the parsing of configuration file is correct.
This patch probably seems useless, it's just a thought to stay coherent
with an uniform behavior.
Yes, I think the usual "programs should not print if the normal
operation went fine" style should keep pfctl -f some-file quiet.
Having output in the specific config test mode would not hurt, but
it's not something I've been longing for.