mac80211: move synchronize_net() before sta key removal

There's no reason to do this inside the sta key removal
since the keys can only be reached through the sta (and
not by the driver at all) so once the sta can no longer
be reached, the keys are safe.

This will allow further optimisation opportunities with
multiple stations.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/sta_info.c

@@ -831,7 +831,8 @@ int __must_check __sta_info_destroy(struct sta_info *sta)
 	    rcu_access_pointer(sdata->u.vlan.sta) == sta)
 		RCU_INIT_POINTER(sdata->u.vlan.sta, NULL);
 
-	/* this always calls synchronize_net() */
+	synchronize_net();
+	/* now keys can no longer be reached */
 	ieee80211_free_sta_keys(local, sta);
 
 	sta->dead = true;