op-node: Fix panic when p2p server fails to start (#4493)

I only set `OpNode.server` to the created server if it starts up
successfully. This alleviates an error where if creation succeeds,
but startup does not, we attempt to stop the server which panics.

This also adds logging to indicate that initialization failed. This
logging primarily benefits users who call `node.New` directly rather
than end users because there is already logging in the main function.

I tested this manually with op-e2e & was able to reproduce the error &
confirm that it is fixed.

op-node/node/node.go

@@ -61,6 +61,7 @@ func New(ctx context.Context, cfg *Config, log log.Logger, snapshotLog log.Logge
 
 	err := n.init(ctx, cfg, snapshotLog)
 	if err != nil {
+		log.Error("Error intializing the rollup node", "err", err)
 		// ensure we always close the node resources if we fail to initialize the node.
 		if closeErr := n.Close(); closeErr != nil {
 			return nil, multierror.Append(err, closeErr)
@@ -162,21 +163,21 @@ func (n *OpNode) initL2(ctx context.Context, cfg *Config, snapshotLog log.Logger
 }
 
 func (n *OpNode) initRPCServer(ctx context.Context, cfg *Config) error {
-	var err error
-	n.server, err = newRPCServer(ctx, &cfg.RPC, &cfg.Rollup, n.l2Source.L2Client, n.l2Driver, n.log, n.appVersion, n.metrics)
+	server, err := newRPCServer(ctx, &cfg.RPC, &cfg.Rollup, n.l2Source.L2Client, n.l2Driver, n.log, n.appVersion, n.metrics)
 	if err != nil {
 		return err
 	}
 	if n.p2pNode != nil {
-		n.server.EnableP2P(p2p.NewP2PAPIBackend(n.p2pNode, n.log, n.metrics))
+		server.EnableP2P(p2p.NewP2PAPIBackend(n.p2pNode, n.log, n.metrics))
 	}
 	if cfg.RPC.EnableAdmin {
-		n.server.EnableAdminAPI(NewAdminAPI(n.l2Driver, n.metrics))
+		server.EnableAdminAPI(NewAdminAPI(n.l2Driver, n.metrics))
 	}
 	n.log.Info("Starting JSON-RPC server")
-	if err := n.server.Start(); err != nil {
+	if err := server.Start(); err != nil {
 		return fmt.Errorf("unable to start RPC server: %w", err)
 	}
+	n.server = server
 	return nil
 }