Bluetooth: Don't enforce authentication for L2CAP PSM 1 and 3

The recommendation for the L2CAP PSM 1 (SDP) is to not use any kind
of authentication or encryption. So don't trigger authentication
for incoming and outgoing SDP connections.

For L2CAP PSM 3 (RFCOMM) there is no clear requirement, but with
Bluetooth 2.1 the initiator is required to enable authentication
and encryption first and this gets enforced. So there is no need
to trigger an additional authentication step. The RFCOMM service
security will make sure that a secure enough link key is present.

When the encryption gets enabled after the SDP connection setup,
then switch the security level from SDP to low security.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>