ath9k: Fix bug in delimiter padding computation

There is a roundng error in delimiter padding computation
which causes severe throughput drop with some of AR9003.
signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Cc:stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -177,8 +177,8 @@ void ath_descdma_cleanup(struct ath_softc *sc, struct ath_descdma *dd,
 
 /* returns delimiter padding required given the packet length */
 #define ATH_AGGR_GET_NDELIM(_len)					\
-	(((((_len) + ATH_AGGR_DELIM_SZ) < ATH_AGGR_MINPLEN) ?           \
-	  (ATH_AGGR_MINPLEN - (_len) - ATH_AGGR_DELIM_SZ) : 0) >> 2)
+       (((_len) >= ATH_AGGR_MINPLEN) ? 0 :                             \
+        DIV_ROUND_UP(ATH_AGGR_MINPLEN - (_len), ATH_AGGR_DELIM_SZ))
 
 #define BAW_WITHIN(_start, _bawsz, _seqno) \
 	((((_seqno) - (_start)) & 4095) < (_bawsz))