Bluetooth: Unregister suspend with userchannel

When HCI_USERCHANNEL is used, unregister the suspend notifier when
binding and register when releasing. The userchannel socket should be
left alone after open is completed.

Signed-off-by: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>