[MAC80211]: filter locally-originated multicast frames

In STA mode, the AP will echo our traffic.  This includes multicast
traffic.

Receiving these frames confuses some protocols and applications,
notably IPv6 Duplicate Address Detection.
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>
Signed-off-by: NJohannes Berg <johannes@sipsolutions.net>
Acked-by: NMichael Wu <flamingice@sourmilk.net>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/mac80211/rx.c

@@ -988,9 +988,10 @@ ieee80211_rx_h_data(struct ieee80211_txrx_data *rx)
 		memcpy(dst, hdr->addr1, ETH_ALEN);
 		memcpy(src, hdr->addr3, ETH_ALEN);
 
-		if (sdata->type != IEEE80211_IF_TYPE_STA) {
+		if (sdata->type != IEEE80211_IF_TYPE_STA ||
+		    (is_multicast_ether_addr(dst) &&
+		     !compare_ether_addr(src, dev->dev_addr)))
 			return TXRX_DROP;
-		}
 		break;
 	case 0:
 		/* DA SA BSSID */