mac80211: optimise mixed AP/VLAN station removal

Teach sta_info_flush() to optionally also remove stations
from all VLANs associated with an AP interface to optimise
the station removal (in particular, synchronize_net().)

To not have to add the vlans argument throughout, do some
refactoring.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index 89d449d..4576ba0 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -960,7 +960,7 @@
 }
 
 
-int sta_info_flush(struct ieee80211_sub_if_data *sdata)
+int __sta_info_flush(struct ieee80211_sub_if_data *sdata, bool vlans)
 {
 	struct ieee80211_local *local = sdata->local;
 	struct sta_info *sta, *tmp;
@@ -969,9 +969,13 @@
 
 	might_sleep();
 
+	WARN_ON(vlans && sdata->vif.type != NL80211_IFTYPE_AP);
+	WARN_ON(vlans && !sdata->bss);
+
 	mutex_lock(&local->sta_mtx);
 	list_for_each_entry_safe(sta, tmp, &local->sta_list, list) {
-		if (sdata == sta->sdata) {
+		if (sdata == sta->sdata ||
+		    (vlans && sdata->bss == sta->sdata->bss)) {
 			if (!WARN_ON(__sta_info_destroy_part1(sta)))
 				list_add(&sta->free_list, &free_list);
 			ret++;