ath9k: fix checks for first subframe delimiter padding

The commit "ath9k_hw: Fix exceed transmission burst-time of 5GHz" added
a padding of 60 delimiters on the first subframe to work around an issue
on AR9380, but it lacked the checks to prevent it from being applied to
pre-AR9380, enterprise AR9380 or AR9580+
Signed-off-by: NFelix Fietkau <nbd@openwrt.org>
Cc: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/reg.h

@@ -1132,7 +1132,7 @@ enum {
 #define AR_INTR_PRIO_ASYNC_ENABLE (AR_SREV_9340(ah) ? 0x4094 : 0x40d4)
 #define AR_ENT_OTP		  0x40d8
 #define AR_ENT_OTP_CHAIN2_DISABLE               0x00020000
-#define AR_ENT_OTP_MPSD		0x00800000
+#define AR_ENT_OTP_MIN_PKT_SIZE_DISABLE		0x00800000
 
 #define AR_CH0_BB_DPLL1		 0x16180
 #define AR_CH0_BB_DPLL1_REFDIV	 0xF8000000

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

@@ -709,7 +709,8 @@ static int ath_compute_num_delims(struct ath_softc *sc, struct ath_atx_tid *tid,
 	 * Add delimiter when using RTS/CTS with aggregation
 	 * and non enterprise AR9003 card
 	 */
-	if (first_subfrm)
+	if (first_subfrm && !AR_SREV_9580_10_OR_LATER(sc->sc_ah) &&
+	    (sc->sc_ah->ent_mode & AR_ENT_OTP_MIN_PKT_SIZE_DISABLE))
 		ndelim = max(ndelim, FIRST_DESC_NDELIMS);
 
 	/*