Bluetooth: Select Basic Mode as default for SOCK_SEQPACKET

The default mode for SOCK_SEQPACKET is Basic Mode. So when no
mode has been specified, Basic Mode shall be used.

This is important for current application to keep working as
expected and not cause a regression.

Signed-off-by: Gustavo F. Padovan <gustavo@las.ic.unicamp.br>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>