mac80211: remove hw.conf.channel usage where possible

Removes hw.conf.channel usage from the following functions:
 * ieee80211_mandatory_rates
 * ieee80211_sta_get_rates
 * ieee80211_frame_duration
 * ieee80211_rts_duration
 * ieee80211_ctstoself_duration

This is in preparation for multi-channel operation.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 32cd517..eff00e6 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -2947,6 +2947,7 @@
  */
 __le16 ieee80211_generic_frame_duration(struct ieee80211_hw *hw,
 					struct ieee80211_vif *vif,
+					enum ieee80211_band band,
 					size_t frame_len,
 					struct ieee80211_rate *rate);