net/mwan3: fix ipset generation in hotplug script with an lock

Fix critical section during hotplug events.

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

net/mwan3/files/etc/hotplug.d/iface/15-mwan3

@@ -12,7 +12,9 @@ if [ "$ACTION" == "ifup" ]; then
         [ -n "$DEVICE" ] || exit 3
 fi
 
+mwan3_lock
 mwan3_set_connected_iptables
+mwan3_unlock
 
 config_load mwan3
 config_get enabled $INTERFACE enabled 0