hostap: Limit only to WPA2 for SAP

Due to AP-MLME being in the host and expensive computation WPA3 is not
working reliably, so, for now this is being disabled.

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