nl80211: send deauth reason if locally generated

Send disconnection reason code to user space even if it's locally
generated, since some tests that check reason code may fail because of
the current behavior.

Signed-off-by: David Spinadel <david.spinadel@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>