Bluetooth: Preserve L2CAP flags values

Previous callers of l2cap_build_conf_rsp in l2cap_config_req use
flags instead of continuation flag hardcoded value. It does not change
logic and preserve future possible flags.

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>