mac802154: util: add stop_device utility function

This patch adds ieee802154_stop_device for preparing a utility function
to stop the ieee802154 device.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
diff --git a/net/mac802154/iface.c b/net/mac802154/iface.c
index 4760368..416de90 100644
--- a/net/mac802154/iface.c
+++ b/net/mac802154/iface.c
@@ -314,11 +314,8 @@
 
 	clear_bit(SDATA_STATE_RUNNING, &sdata->state);
 
-	if (!local->open_count) {
-		flush_workqueue(local->workqueue);
-		hrtimer_cancel(&local->ifs_timer);
-		drv_stop(local);
-	}
+	if (!local->open_count)
+		ieee802154_stop_device(local);
 
 	return 0;
 }