Bluetooth: Add an extra check in mgmt_device_disconnected()

This patch adds an extra check in mgmt_device_disconnected() so we only
send the "Device Disconnected" event if it is ACL_LINK or LE_LINK link
type.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>