mac80211: extend set_coverage_class signature

Extend mac80211 set_coverage_class API in order to enable ACK timeout
estimation algorithm (dynack) passing coverage class equals to -1
to lower drivers. Synchronize set_coverage_class routine signature with
mac80211 function pointer for p54, ath9k, ath9k_htc and ath5k drivers.

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi83@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index db4975c..c6e6a68 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -2673,7 +2673,9 @@
  *
  * @set_coverage_class: Set slot time for given coverage class as specified
  *	in IEEE 802.11-2007 section 17.3.8.6 and modify ACK timeout
- *	accordingly. This callback is not required and may sleep.
+ *	accordingly; coverage class equals to -1 to enable ACK timeout
+ *	estimation algorithm (dynack). To disable dynack set valid value for
+ *	coverage class. This callback is not required and may sleep.
  *
  * @testmode_cmd: Implement a cfg80211 test mode command. The passed @vif may
  *	be %NULL. The callback can sleep.
@@ -2957,7 +2959,7 @@
 	int (*get_survey)(struct ieee80211_hw *hw, int idx,
 		struct survey_info *survey);
 	void (*rfkill_poll)(struct ieee80211_hw *hw);
-	void (*set_coverage_class)(struct ieee80211_hw *hw, u8 coverage_class);
+	void (*set_coverage_class)(struct ieee80211_hw *hw, s16 coverage_class);
 #ifdef CONFIG_NL80211_TESTMODE
 	int (*testmode_cmd)(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
 			    void *data, int len);