Bluetooth: Fix checking for valid disconnect parameters in unpair_device

The valid values for the Disconnect parameter in the Unpair Device
command are 0x00 and 0x01. If any other value is encountered the command
should fail with the appropriate invalid params response.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>