mac80211: split IBSS/managed code

This patch splits out the ibss code and data from managed (station) mode.
The reason to do this is to better separate the state machines, and have
the code be contained better so it gets easier to determine what exactly
a given change will affect, that in turn makes it easier to understand.

This is quite some churn, especially because I split sdata->u.sta into
sdata->u.mgd and sdata->u.ibss, but I think it's easier to maintain that
way. I've also shuffled around some code -- null function sending is only
applicable to managed interfaces so put that into that file, some other
functions are needed from various places so put them into util, and also
rearranged the prototypes in ieee80211_i.h accordingly.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/ht.c b/net/mac80211/ht.c
index 82ea0b6..69b6e9a 100644
--- a/net/mac80211/ht.c
+++ b/net/mac80211/ht.c
@@ -169,7 +169,6 @@
 			  u16 initiator, u16 reason_code)
 {
 	struct ieee80211_local *local = sdata->local;
-	struct ieee80211_if_sta *ifsta = &sdata->u.sta;
 	struct sk_buff *skb;
 	struct ieee80211_mgmt *mgmt;
 	u16 params;
@@ -190,8 +189,9 @@
 	if (sdata->vif.type == NL80211_IFTYPE_AP ||
 	    sdata->vif.type == NL80211_IFTYPE_AP_VLAN)
 		memcpy(mgmt->bssid, sdata->dev->dev_addr, ETH_ALEN);
-	else
-		memcpy(mgmt->bssid, ifsta->bssid, ETH_ALEN);
+	else if (sdata->vif.type == NL80211_IFTYPE_STATION)
+		memcpy(mgmt->bssid, sdata->u.mgd.bssid, ETH_ALEN);
+
 	mgmt->frame_control = cpu_to_le16(IEEE80211_FTYPE_MGMT |
 					  IEEE80211_STYPE_ACTION);