mac80211: dont use interface indices in drivers

This patch gets rid of the if_id stuff where possible in favour of
a new per-virtual-interface structure "struct ieee80211_vif". This
structure is located at the end of the per-interface structure and
contains a variable length driver-use data area.

This has two advantages:
 * removes the need to look up interfaces by if_id, this is better
   for working with network namespaces and performance
 * allows drivers to store and retrieve per-interface data without
   having to allocate own lists/hash tables

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath5k/hw.c b/drivers/net/wireless/ath5k/hw.c
index 5623d7d..3b93363 100644
--- a/drivers/net/wireless/ath5k/hw.c
+++ b/drivers/net/wireless/ath5k/hw.c
@@ -533,7 +533,7 @@
 		 * ieee80211_duration() for a brief description of
 		 * what rate we should choose to TX ACKs. */
 		tx_time = ieee80211_generic_frame_duration(sc->hw,
-			sc->iface_id, 10, control_rate->rate_kbps/100);
+			sc->vif, 10, control_rate->rate_kbps/100);
 
 		ath5k_hw_reg_write(ah, tx_time, reg);