carl9170: fix spurious restart due to high latency

RX Stress tests of unidirectional bulk traffic with
bitrates of up to 220Mbit/s have revealed that the
fatal-event recovery logic [which was solely triggered
by an out-of-rx-buffer situation] is too aggressive.

The new method now "pings" the device and then
decides - based on the response - whenever
a restart is needed or not.

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/carl9170/usb.c b/drivers/net/wireless/ath/carl9170/usb.c
index d8607f4..ddf5373 100644
--- a/drivers/net/wireless/ath/carl9170/usb.c
+++ b/drivers/net/wireless/ath/carl9170/usb.c
@@ -431,7 +431,7 @@
 			 * device.
 			 */
 
-			carl9170_restart(ar, CARL9170_RR_SLOW_SYSTEM);
+			ieee80211_queue_work(ar->hw, &ar->ping_work);
 		}
 	} else {
 		/*