ath9k: validate for non-zero BSSID

before concluding that the recieved beacon is for us, let us make sure
that the BSSID is non-zero. when I configured ad-hoc mode as creator and
left it for some time without joining I found we recieved few frames whose
BSSID is zero, which we concluded wrongly as 'my_beacons'

Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/recv.c

@@ -1823,6 +1823,7 @@ int ath_rx_tasklet(struct ath_softc *sc, int flush, bool hp)
 		hdr = (struct ieee80211_hdr *) (hdr_skb->data + rx_status_len);
 		rxs = IEEE80211_SKB_RXCB(hdr_skb);
 		if (ieee80211_is_beacon(hdr->frame_control) &&
+		    !is_zero_ether_addr(common->curbssid) &&
 		    !compare_ether_addr(hdr->addr3, common->curbssid))
 			rs.is_mybeacon = true;
 		else