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>

drivers/net/wireless/b43/xmit.c

@@ -290,7 +290,8 @@ int b43_generate_txhdr(struct b43_wldev *dev,
 		txhdr->dur_fb = wlhdr->duration_id;
 	} else {
 		txhdr->dur_fb = ieee80211_generic_frame_duration(
-			dev->wl->hw, info->control.vif, fragment_len, fbrate);
+			dev->wl->hw, info->control.vif, info->band,
+			fragment_len, fbrate);
 	}
 
 	plcp_fragment_len = fragment_len + FCS_LEN;