mac80211: use RCU_INIT_POINTER

rcu_assign_pointer() ensures that the initialization of a structure is
carried out before storing a pointer to that structure. However, in the
case that NULL is assigned there's no structure to initialize so using
RCU_INIT_POINTER instead is safe and more efficient.

Signed-off-by: Monam Agarwal <monamagarwal123@gmail.com>
[squash eight tiny patches, rewrite commit log]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/util.c b/net/mac80211/util.c
index 5cf62ec..73af739 100644
--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c
@@ -1546,7 +1546,7 @@
 		WARN_ON(local->resuming);
 		res = drv_add_interface(local, sdata);
 		if (WARN_ON(res)) {
-			rcu_assign_pointer(local->monitor_sdata, NULL);
+			RCU_INIT_POINTER(local->monitor_sdata, NULL);
 			synchronize_net();
 			kfree(sdata);
 		}