mac80211: Add new callback set_coverage_class

Mac80211 callback to driver set_coverage_class() sets slot time and ACK
timeout for given IEEE 802.11 coverage class. The callback is optional,
but it's essential for long distance links.

Signed-off-by: Lukas Turek <8an@praha12.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index 2e5e841..976014c 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -1230,6 +1230,13 @@
 	struct ieee80211_local *local = wiphy_priv(wiphy);
 	int err;
 
+	if (changed & WIPHY_PARAM_COVERAGE_CLASS) {
+		err = drv_set_coverage_class(local, wiphy->coverage_class);
+
+		if (err)
+			return err;
+	}
+
 	if (changed & WIPHY_PARAM_RTS_THRESHOLD) {
 		err = drv_set_rts_threshold(local, wiphy->rts_threshold);