ath9k_hw: fix A-MPDU key search issues on AR9003

Under load, a large number of frames can produce decryption errors, even when
no key cache update is being done. Performing a key search for every single
frame in an A-MPDU improves reliability.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/hw.c b/drivers/net/wireless/ath/ath9k/hw.c
index fd4fdb5..c686987 100644
--- a/drivers/net/wireless/ath/ath9k/hw.c
+++ b/drivers/net/wireless/ath/ath9k/hw.c
@@ -1817,6 +1817,10 @@
 
 	ah->misc_mode |= AR_PCU_MIC_NEW_LOC_ENA;
 
+	/* enable key search for every frame in an aggregate */
+	if (AR_SREV_9300_20_OR_LATER(ah))
+		ah->misc_mode |= AR_PCU_ALWAYS_PERFORM_KEYSEARCH;
+
 	pCap->low_2ghz_chan = 2312;
 	pCap->high_2ghz_chan = 2732;