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/net/mac80211/tx.c b/net/mac80211/tx.c
index 4f6aac1..0abbef95 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -159,7 +159,7 @@
 		/* Time needed to transmit ACK
 		 * (10 bytes + 4-byte FCS = 112 bits) plus SIFS; rounded up
 		 * to closest integer */
-		dur = ieee80211_frame_duration(local, 10, rate, erp,
+		dur = ieee80211_frame_duration(sband->band, 10, rate, erp,
 				tx->sdata->vif.bss_conf.use_short_preamble);
 
 	if (next_frag_len) {
@@ -167,7 +167,7 @@
 		 * transmit next fragment plus ACK and 2 x SIFS. */
 		dur *= 2; /* ACK + SIFS */
 		/* next fragment */
-		dur += ieee80211_frame_duration(local, next_frag_len,
+		dur += ieee80211_frame_duration(sband->band, next_frag_len,
 				txrate->bitrate, erp,
 				tx->sdata->vif.bss_conf.use_short_preamble);
 	}