wl1271: Allocate TX descriptors more efficiently

On each TX descriptor allocation, a free entry is found by traversing the TX
descriptors array.

Improve this by holding a bitmap of all TX descriptors, and using efficient
bit operations to search for free entries.

Signed-off-by: Ido Yariv <ido@wizery.com>
Reviewed-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
diff --git a/drivers/net/wireless/wl12xx/wl1271.h b/drivers/net/wireless/wl12xx/wl1271.h
index 4a034a3..718e96d 100644
--- a/drivers/net/wireless/wl12xx/wl1271.h
+++ b/drivers/net/wireless/wl12xx/wl1271.h
@@ -398,6 +398,7 @@
 	struct work_struct tx_work;
 
 	/* Pending TX frames */
+	unsigned long tx_frames_map[BITS_TO_LONGS(ACX_TX_DESCRIPTORS)];
 	struct sk_buff *tx_frames[ACX_TX_DESCRIPTORS];
 	int tx_frames_cnt;