code: func (client *cniClient) CleanupNS(
  	ctx context.Context,
  	cfg *Config,
  	timeout time.Duration) error {
  
  	derivedCtx, cancel := context.WithTimeout(ctx, timeout)
  	defer cancel()
  
  	err := make(chan error)
  	go func(err chan error) {
  		err <- client.cleanupNS(cfg)
  	}(err)
  
  	select {
  	case <-derivedCtx.Done():
  		return errors.Wrap(derivedCtx.Err(), "cni cleanup: container namespace cleanup failed")
  	case err := <-err:
  		return err
  	}
  }
docs: // CleanupNS will clean up the container namespace, including remove the veth
  // pair and stop the dhclient