*** ATTENTION ***

To run arpwatch from startup, add
arpwatch_enable="YES" to /etc/rc.conf

Available variables you add/set to /etc/rc.conf.
- arpwatch_enable (bool):      Set to "NO" by default.
                               Set it to "YES" to enable arpwatch.
- arpwatch_flags (str):        Set to "-N" by default.
                               Extra flags passed to start command.