ath9k_hw: Fix TX interrupt mitigation settings

TX interrupt mitigation reduces the number of interrupts
by addressing several interrupt actions (AR_IMR_TXOK,
AR_IMR_TXDESC) all in one interrupt so when enabling
it discard setting the other interrupts.

Without this TX interrupt mitigation would actually
increase the number of interrupts two-fold. We still
leave TX interrupt mitigation disabled as it is still
being tested.
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -878,10 +878,12 @@ enum ath9k_int ath9k_hw_set_interrupts(struct ath_hw *ah,
 	if (ints & ATH9K_INT_TX) {
 		if (ah->config.tx_intr_mitigation)
 			mask |= AR_IMR_TXMINTR | AR_IMR_TXINTM;
-		if (ah->txok_interrupt_mask)
-			mask |= AR_IMR_TXOK;
-		if (ah->txdesc_interrupt_mask)
-			mask |= AR_IMR_TXDESC;
+		else {
+			if (ah->txok_interrupt_mask)
+				mask |= AR_IMR_TXOK;
+			if (ah->txdesc_interrupt_mask)
+				mask |= AR_IMR_TXDESC;
+		}
 		if (ah->txerr_interrupt_mask)
 			mask |= AR_IMR_TXERR;
 		if (ah->txeol_interrupt_mask)