mac80211: advertise support for full station state in AP mode

This enables adding stations in unauthenticated mode, just after
receiving the first authentication frame; which in turn allows
sending a negative authentication reply if the station cannot be
added.

In addition init rate control for unassociated station only when
it becomes associated, prior to that low rates will be used.

Signed-off-by: Ayala Beker <ayala.beker@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>