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/ath5k.h b/drivers/net/wireless/ath/ath5k/ath5k.h
index ae311d2..66bcb50 100644
--- a/drivers/net/wireless/ath/ath5k/ath5k.h
+++ b/drivers/net/wireless/ath/ath5k/ath5k.h
@@ -1063,6 +1063,7 @@
 	u32			ah_cw_min;
 	u32			ah_cw_max;
 	u32			ah_limit_tx_retries;
+	u8			ah_coverage_class;
 
 	/* Antenna Control */
 	u32			ah_ant_ctl[AR5K_EEPROM_N_MODES][AR5K_ANT_MAX];
@@ -1200,6 +1201,7 @@
 
 /* Protocol Control Unit Functions */
 extern int ath5k_hw_set_opmode(struct ath5k_hw *ah);
+extern void ath5k_hw_set_coverage_class(struct ath5k_hw *ah, u8 coverage_class);
 /* BSSID Functions */
 extern int ath5k_hw_set_lladdr(struct ath5k_hw *ah, const u8 *mac);
 extern void ath5k_hw_set_associd(struct ath5k_hw *ah);