cfg80211: warn again on spurious deauth

The original code in mac80211 could send a deauth
frame under certain circumstances even if nothing
had ever requested an authentication. This has been
fixed with the rework there, so cfg80211 can now
warn again about spurious events to catch possible
future drivers or mac80211 regressions.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>