Bluetooth: Add missing error handling for Set Connectable

If the HCI commands related to the Set Connectable command fail we will
get a non-zero status in the request completion callback. In such a case
we must respond with the appropriate command status message to user space.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>