wl1251: Fix queue stopping/waking for TX path

This patch was adapted from 06f7bc7db79fabe6b2ec16eff0f59e4acc21eb72
(from linus's linux-2.6 tree of kernel.org)

here's the original message:
    The queue stopping/waking functionality was broken in a way that could
    cause huge latencies in TX transfers and even cause the TX to stall in the
    right circumstances. Correct these problems.

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@no-log.org>
Acked-by: Kalle Valo <kvalo@adurom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/wl12xx/wl1251.h b/drivers/net/wireless/wl12xx/wl1251.h
index 9bc4fea3..e113d4c 100644
--- a/drivers/net/wireless/wl12xx/wl1251.h
+++ b/drivers/net/wireless/wl12xx/wl1251.h
@@ -272,6 +272,8 @@
 	int irq;
 	bool use_eeprom;
 
+	spinlock_t wl_lock;
+
 	enum wl1251_state state;
 	struct mutex mutex;
 
@@ -399,7 +401,8 @@
 
 #define WL1251_DEFAULT_POWER_LEVEL 20
 
-#define WL1251_TX_QUEUE_MAX_LENGTH 20
+#define WL1251_TX_QUEUE_LOW_WATERMARK  10
+#define WL1251_TX_QUEUE_HIGH_WATERMARK 25
 
 #define WL1251_DEFAULT_BEACON_INT 100
 #define WL1251_DEFAULT_DTIM_PERIOD 1