cfg80211: add channel tracking for AP and mesh

We need to know which channel is used by a running
AP and mesh for channel context accounting and
finding matching/active interface combination.

STA/IBSS have current_bss already which allows us
to check which channel a vif is tuned to.
Non-fixed channel IBSS can be handled with
additional changes.

Monitor mode is going to be handled differently.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/wireless/ap.c b/net/wireless/ap.c
index 45199cc..fcc60d8 100644
--- a/net/wireless/ap.c
+++ b/net/wireless/ap.c
@@ -24,8 +24,10 @@
 		return -ENOENT;
 
 	err = rdev->ops->stop_ap(&rdev->wiphy, dev);
-	if (!err)
+	if (!err) {
 		wdev->beacon_interval = 0;
+		wdev->channel = NULL;
+	}
 
 	return err;
 }