mac80211: stay authenticated after disassoc

After being disassociated by the AP, mac80211 currently
reports this to cfg80211, and then goes to delete the
association. That's fine, but cfg80211 assumes that it's
still authenticated, however, mac80211 throws away all
state.

This fixes mac80211 to keep track of the authentication
in that case so that cfg80211 can request a deauth or
new association properly.

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