pf: Return non-zero from 'status' if pf is not enabled
In the pf rc.d script the output of /etc/rc.d/pf status or `/etc/rc.d/pf
onestatus` always provided an exit status of zero. This made it fiddly to
programmatically determine if pf was running or not.
Return a non-zero status if the pf module is not loaded, extend pfctl to have
an option to return an error status if pf is not enabled.
Submitted by: James Park-Watt <jimmypw AT gmail.com>