olsrd: hotplug: dont test if daemon is enabled, but look for a written PID-file. this solves the issue, that hotplug fires multiple restarts during boot for each upcoming interface (e.g. lo, lan, wan, wifi1, wifi2) which is racy somehow, but leaves hotplug itself working after normal startup. also reduce forking by directly sourcing '/etc/init.d/olsrd' via rc.common