cfg80211: fix dangling scan request checking

My patch "cfg80211: fix deadlock" broke the code it
was supposed to fix, the scan request checking. But
it's not trivial to put it back the way it was, since
the original patch had a deadlock.

Now do it in a completely new way: queue the check
off to a work struct, where we can freely lock. But
that has some more complications, like needing to
wait for it to be done before the wiphy/rdev can be
destroyed, so some code is required to handle that.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index 0b146bb..3d874c6 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -1325,6 +1325,8 @@
 
 	struct mutex mtx;
 
+	struct work_struct cleanup_work;
+
 	/* currently used for IBSS and SME - might be rearranged later */
 	u8 ssid[IEEE80211_MAX_SSID_LEN];
 	u8 ssid_len;