mac80211: move beacon_loss_count into ifmgd

There's little point in keeping (and even sending to userspace)
the beacon_loss_count value per station, since it can only apply
to the AP on a managed-mode connection. Move the value to ifmgd,
advertise it only in managed mode, and remove it from ethtool as
it's available through better interfaces.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/ieee80211_i.h

@@ -503,6 +503,9 @@ struct ieee80211_if_managed {
 	 */
 	unsigned int count_beacon_signal;
 
+	/* Number of times beacon loss was invoked. */
+	unsigned int beacon_loss_count;
+
 	/*
 	 * Last Beacon frame signal strength average (ave_beacon_signal / 16)
 	 * that triggered a cqm event. 0 indicates that no event has been