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/ibss.c b/net/mac80211/ibss.c
index 06d2878..35e4f94 100644
--- a/net/mac80211/ibss.c
+++ b/net/mac80211/ibss.c
@@ -253,7 +253,7 @@
 
 	presp = rcu_dereference_protected(ifibss->presp,
 					  lockdep_is_held(&sdata->wdev.mtx));
-	rcu_assign_pointer(ifibss->presp, NULL);
+	RCU_INIT_POINTER(ifibss->presp, NULL);
 	if (presp)
 		kfree_rcu(presp, rcu_head);