code: func (s *Sandbox) NetNsJoin(nspath, name string) error {
  	if s.netns != nil {
  		return fmt.Errorf("sandbox already has a network namespace, cannot join another")
  	}
  
  	netNS, err := s.NetNsGet(nspath, name)
  	if err != nil {
  		return err
  	}
  
  	s.netns = netNS
  
  	return nil
  }
docs: // NetNsJoin attempts to join the sandbox to an existing network namespace
  // This will fail if the sandbox is already part of a network namespace