mac80211: exit cooked monitor RX early if there are none

If there are no cooked monitor interfaces, there's
no point in building the radiotap RX header for the
frame and iterating the interface list.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/rx.c

@@ -2489,6 +2489,10 @@ static void ieee80211_rx_cooked_monitor(struct ieee80211_rx_data *rx,
 		goto out_free_skb;
 	rx->flags |= IEEE80211_RX_CMNTR;
 
+	/* If there are no cooked monitor interfaces, just free the SKB */
+	if (!local->cooked_mntrs)
+		goto out_free_skb;
+
 	if (skb_headroom(skb) < sizeof(*rthdr) &&
 	    pskb_expand_head(skb, sizeof(*rthdr), 0, GFP_ATOMIC))
 		goto out_free_skb;