ath9k: Fix STA disconnect issue due to received MIC failed bcast frames

AR_RxKeyIdxValid will not be set for bcast/mcast frames and so relying
this status for MIC failed frames is buggy.

Due to this, MIC failure events for broadcast frames are not sent to
supplicant resulted in AP disconnecting the STA.

Able to pass Wifi Test case 5.2.18 with this fix.

Cc: Stable <stable@kernel.org> (2.6.36+)
Signed-off-by: Senthil Balasubramanian <senthilkumar@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -703,8 +703,7 @@ int ath9k_hw_rxprocdesc(struct ath_hw *ah, struct ath_desc *ds,
 			rs->rs_phyerr = phyerr;
 		} else if (ads.ds_rxstatus8 & AR_DecryptCRCErr)
 			rs->rs_status |= ATH9K_RXERR_DECRYPT;
-		else if ((ads.ds_rxstatus8 & AR_MichaelErr) &&
-		         rs->rs_keyix != ATH9K_RXKEYIX_INVALID)
+		else if (ads.ds_rxstatus8 & AR_MichaelErr)
 			rs->rs_status |= ATH9K_RXERR_MIC;
 		else if (ads.ds_rxstatus8 & AR_KeyMiss)
 			rs->rs_status |= ATH9K_RXERR_DECRYPT;

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

@@ -1049,9 +1049,11 @@ static void ath9k_rx_skb_postprocess(struct ath_common *common,
 	int hdrlen, padpos, padsize;
 	u8 keyix;
 	__le16 fc;
+	bool is_mc;
 
 	/* see if any padding is done by the hw and remove it */
 	hdr = (struct ieee80211_hdr *) skb->data;
+	is_mc = !!is_multicast_ether_addr(hdr->addr1);
 	hdrlen = ieee80211_get_hdrlen_from_skb(skb);
 	fc = hdr->frame_control;
 	padpos = ath9k_cmn_padpos(hdr->frame_control);
@@ -1072,7 +1074,7 @@ static void ath9k_rx_skb_postprocess(struct ath_common *common,
 
 	keyix = rx_stats->rs_keyix;
 
-	if (!(keyix == ATH9K_RXKEYIX_INVALID) && !decrypt_error &&
+	if ((is_mc || !(keyix == ATH9K_RXKEYIX_INVALID)) && !decrypt_error &&
 	    ieee80211_has_protected(fc)) {
 		rxs->flag |= RX_FLAG_DECRYPTED;
 	} else if (ieee80211_has_protected(fc)