ath9k: fix queue depth accounting in ath_tx_txqaddbuf

ath_tx_txqaddbuf assumes that all the linked buffers in the queue passed
to it are part of the same A-MPDU or MPDU. The CAB queue rework violates
this assumption, which can cause the internal queue depth to go
negative.
Fix this by increasing the counter for all slots of [bf, bf->bf_lastbf]

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -1778,9 +1778,13 @@ static void ath_tx_txqaddbuf(struct ath_softc *sc, struct ath_txq *txq,
 	}
 
 	if (!internal) {
-		txq->axq_depth++;
-		if (bf_is_ampdu_not_probing(bf))
-			txq->axq_ampdu_depth++;
+		while (bf) {
+			txq->axq_depth++;
+			if (bf_is_ampdu_not_probing(bf))
+				txq->axq_ampdu_depth++;
+
+			bf = bf->bf_lastbf->bf_next;
+		}
 	}
 }