ath9k: fix a WEP crypto related regression

commit b4a82a0 "ath9k_hw: fix interpretation of the rx KeyMiss flag"
fixed the interpretation of the KeyMiss flag for keycache based lookups,
however WEP encryption uses a static index, so KeyMiss is always asserted
for it, even though frames are decrypted properly.
Fix this by clearing the ATH9K_RXERR_KEYMISS flag if no keycache based
lookup was performed.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Cc: stable@vger.kernel.org
Reported-by: Laurent Bonnans <bonnans.l@gmail.com>
Reported-by: Jurica Vukadin <u.ra604@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -822,6 +822,14 @@ static bool ath9k_rx_accept(struct ath_common *common,
 		(ATH9K_RXERR_DECRYPT | ATH9K_RXERR_CRC | ATH9K_RXERR_MIC |
 		 ATH9K_RXERR_KEYMISS));
 
+	/*
+	 * Key miss events are only relevant for pairwise keys where the
+	 * descriptor does contain a valid key index. This has been observed
+	 * mostly with CCMP encryption.
+	 */
+	if (rx_stats->rs_keyix == ATH9K_RXKEYIX_INVALID)
+		rx_stats->rs_status &= ~ATH9K_RXERR_KEYMISS;
+
 	if (!rx_stats->rs_datalen)
 		return false;
         /*