cfg80211: deauth doesn't always imply disconnect

When an AP sends a deauth frame, or we send one
to an AP, that only means we lost our connection
if we were actually connected to that AP. Check
this to avoid sending spurious "disconnected"
events and breaking "iw ... link" reporting.

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