Bluetooth: controller: Send disconnect complete when CIS is terminated

Previously the host would handle disconnecting associated CISes and
invoking callbacks when a host ACL conn was disconnected.

This responsibility has now been moved to the controller, which needs to
send a NODE_RX_TYPE_TERMINATE with the CIS handle for proper
disconnection in the host. This is in accordance with the spec.

As disconnect reason, the CIS uses the ACL reason, which is passed to
the host along with the handle.

Signed-off-by: Morten Priess <mtpr@oticon.com>