Bluetooth: Ignore key unauthenticated for high security

High security level for pre v2.1 devices requires combination link key
authenticated by at least 16 digit PIN code.

It's also necessary to update key_type and pin_length when the key
exists and is sufficently secured for the connection as there will be
no link key notify event in that case.

Signed-off-by: Waldemar Rymarkiewicz <waldemar.rymarkiewicz@tieto.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>