Fix nw sandbox leak when stopping detached container

Signed-off-by: Ryan Liu <ryanlyy@me.com>

daemon/container_operations.go

@@ -916,7 +916,7 @@ func (daemon *Daemon) releaseNetwork(container *container.Container) {
 	settings := container.NetworkSettings.Networks
 	container.NetworkSettings.Ports = nil
 
-	if sid == "" || len(settings) == 0 {
+	if sid == "" {
 		return
 	}