op-node: Default to no netrestrict instead of allow none

When p2p.netrestrict was not set, the empty string was being used as the list of allowed nodes, thus preventing any peers from connecting.

op-node/flags/p2p_flags.go

@@ -156,7 +156,6 @@ var (
 		Name:     "p2p.netrestrict",
 		Usage:    "Comma-separated list of CIDR masks. P2P will only try to connect on these networks",
 		Required: false,
-		Value:    "",
 		EnvVars:  p2pEnv("NETRESTRICT"),
 	}
 	HostMux = &cli.StringFlag{

op-node/p2p/cli/load_config.go

@@ -194,13 +194,14 @@ func loadDiscoveryOpts(conf *p2p.Config, ctx *cli.Context) error {
 		conf.Bootnodes = p2p.DefaultBootnodes
 	}
 
-	netRestrict, err := netutil.ParseNetlist(ctx.String(flags.NetRestrict.Name))
-	if err != nil {
-		return fmt.Errorf("failed to parse net list: %w", err)
+	if ctx.IsSet(flags.NetRestrict.Name) {
+		netRestrict, err := netutil.ParseNetlist(ctx.String(flags.NetRestrict.Name))
+		if err != nil {
+			return fmt.Errorf("failed to parse net list: %w", err)
+		}
+		conf.NetRestrict = netRestrict
 	}
 
-	conf.NetRestrict = netRestrict
-
 	return nil
 }