ath5k: Implement mac80211 callback set_coverage_class

The callback sets slot time as specified in IEEE 802.11-2007 section
17.3.8.6 (for 20MHz channels only for now) and raises ACK and CTS
timeouts accordingly. The values are persistent, they are restored after
device reset.

Signed-off-by: Lukas Turek <8an@praha12.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath5k/reset.c b/drivers/net/wireless/ath/ath5k/reset.c
index 299b33a..6690923 100644
--- a/drivers/net/wireless/ath/ath5k/reset.c
+++ b/drivers/net/wireless/ath/ath5k/reset.c
@@ -1316,6 +1316,10 @@
 	/* Restore antenna mode */
 	ath5k_hw_set_antenna_mode(ah, ah->ah_ant_mode);
 
+	/* Restore slot time and ACK timeouts */
+	if (ah->ah_coverage_class > 0)
+		ath5k_hw_set_coverage_class(ah, ah->ah_coverage_class);
+
 	/*
 	 * Configure QCUs/DCUs
 	 */