hostap: Always allow disconnect

Even if the interface is not in connected state, allow disconnect to be
accepted, this behaviour regressed when the mode check was introduced
and if not connected then SSID will be NULL.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>
Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>