mac80211: don't look up stations for multicast addresses

Since multicast addresses don't exist as stations, don't attempt
to look them up in the hashtable on TX.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/tx.c

@@ -1172,7 +1172,7 @@ ieee80211_tx_prepare(struct ieee80211_sub_if_data *sdata,
 		   tx->sdata->control_port_protocol == tx->skb->protocol) {
 		tx->sta = sta_info_get_bss(sdata, hdr->addr1);
 	}
-	if (!tx->sta)
+	if (!tx->sta && !is_multicast_ether_addr(hdr->addr1))
 		tx->sta = sta_info_get(sdata, hdr->addr1);
 
 	if (tx->sta && ieee80211_is_data_qos(hdr->frame_control) &&