mac80211: disable beacons before removing the associated interface

When downing interfaces, it's a good idea to tell the driver to
stop sending beacons; that way the driver doesn't need special
code in ops->remove_interface() when it should already handle the
case in bss_info_changed().

This fixes a potential crash with at least ath5k since the vif
pointer will be nullified while beacon interrupts are still active.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/pm.c b/net/mac80211/pm.c
index 5e3d476..3320f7d 100644
--- a/net/mac80211/pm.c
+++ b/net/mac80211/pm.c
@@ -96,6 +96,10 @@
 		if (!netif_running(sdata->dev))
 			continue;
 
+		/* disable beaconing */
+		ieee80211_bss_info_change_notify(sdata,
+			BSS_CHANGED_BEACON_ENABLED);
+
 		conf.vif = &sdata->vif;
 		conf.type = sdata->vif.type;
 		conf.mac_addr = sdata->dev->dev_addr;