code: func (s *Stack) Forwarding() bool {
  	// TODO(igudger, bgeffon): Expose via /proc/sys/net/ipv4/ip_forward.
  	s.mu.RLock()
  	defer s.mu.RUnlock()
  	return s.forwarding
  }
docs: // Forwarding returns if the packet forwarding between NICs is enabled.