code: func (ncc *SeesawNCC) RouteDefaultIPv4(unused int, gateway *net.IP) error {
  	ip, err := routeDefaultIPv4()
  	if err != nil {
  		return err
  	}
  	if gateway != nil {
  		*gateway = make(net.IP, len(ip))
  		copy(*gateway, ip)
  	}
  	return nil
  }
docs: // RouteDefaultIPv4 returns the default route for IPv4 traffic.