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/net/mac80211/ieee80211_iface.c b/net/mac80211/ieee80211_iface.c
index 7cfd866..b720663 100644
--- a/net/mac80211/ieee80211_iface.c
+++ b/net/mac80211/ieee80211_iface.c
@@ -47,7 +47,7 @@
 	int ret;
 
 	ASSERT_RTNL();
-	ndev = alloc_netdev(sizeof(struct ieee80211_sub_if_data),
+	ndev = alloc_netdev(sizeof(*sdata) + local->hw.vif_data_size,
 			    name, ieee80211_if_setup);
 	if (!ndev)
 		return -ENOMEM;