cmd: extend dumpgenesis to support network flags on the cmd (#22406)

cmd/geth/chaincmd.go

@@ -62,7 +62,11 @@ It expects the genesis file as argument.`,
 		Usage:     "Dumps genesis block JSON configuration to stdout",
 		ArgsUsage: "",
 		Flags: []cli.Flag{
-			utils.DataDirFlag,
+			utils.MainnetFlag,
+			utils.RopstenFlag,
+			utils.RinkebyFlag,
+			utils.GoerliFlag,
+			utils.YoloV3Flag,
 		},
 		Category: "BLOCKCHAIN COMMANDS",
 		Description: `
@@ -227,6 +231,7 @@ func initGenesis(ctx *cli.Context) error {
 }
 
 func dumpGenesis(ctx *cli.Context) error {
+	// TODO(rjl493456442) support loading from the custom datadir
 	genesis := utils.MakeGenesis(ctx)
 	if genesis == nil {
 		genesis = core.DefaultGenesisBlock()