mac802154: add synchronization handling

This patch adds synchronization handling in start and stop driver ops
calls. This patch is mostly grab from mac80211 which was introduced by
commit ea77f12f ("mac80211: remove
tasklet enable/disable"). This is to be sure that we don't run into same
issues.
Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/mac802154/driver-ops.h

@@ -30,6 +30,7 @@ static inline int drv_start(struct ieee802154_local *local)
 	might_sleep();
 
 	local->started = true;
+	smp_mb();
 
 	return local->ops->start(&local->hw);
 }
@@ -40,6 +41,12 @@ static inline void drv_stop(struct ieee802154_local *local)
 
 	local->ops->stop(&local->hw);
 
+	/* sync away all work on the tasklet before clearing started */
+	tasklet_disable(&local->tasklet);
+	tasklet_enable(&local->tasklet);
+
+	barrier();
+
 	local->started = false;
 }