mwan3: lock critical section on mwan3 down

Signed-off-by: Florian Eckert <fe@dev.tdt.de>

net/mwan3/files/usr/sbin/mwan3

@@ -136,6 +136,8 @@ stop()
 {
 	local ipset route rule table IP IPT pid
 
+	mwan3_lock
+
 	for pid in $(pgrep -f "mwan3rtmon"); do
 		kill -TERM "$pid" > /dev/null 2>&1
 		sleep 1
@@ -184,6 +186,8 @@ stop()
 		$IPS -q destroy $ipset
 	done
 
+	mwan3_unlock
+
 	mwan3_lock_clean
 	rm -rf $MWAN3_STATUS_DIR $MWAN3TRACK_STATUS_DIR