code: func setNAT(ctx *cli.Context, cfg *p2p.Config) {
  	if ctx.GlobalIsSet(NATFlag.Name) {
  		natif, err := nat.Parse(ctx.GlobalString(NATFlag.Name))
  		if err != nil {
  			Fatalf("Option %s: %v", NATFlag.Name, err)
  		}
  		cfg.NAT = natif
  	}
  }
docs: // setNAT creates a port mapper from command line flags.