Teach periodic(8) security output to display information about blocked
packet counts by pf(4).

This adds a ``daily_status_security_pfdenied_enable'' variable to
periodic.conf, which defaults to ``YES'' as the matching IPF(W) versions.

The output will look like this (line wrapped):

pf denied packets:
> block drop log on rl0 proto tcp all [ Evaluations: 504986 Packets: 0
  Bytes: 0 States: 0 ]
> block drop log on rl0 all [ Evaluations: 18559 Packets: 427 Bytes: 140578
  States: 0 ]

Submitted by: clive (thanks a lot!)
MFC after: 2 weeks