Bluetooth: Add SOCK_STREAM support to L2CAP

if enable_ertm is true and we have SOCK_STREAM the default mode will be
ERTM, otherwise Basic Mode.

Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>
Reviewed-by: João Paulo Rechi Vita <jprvita@profusion.mobi>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>