cmd/utils: fix parsing BootstrapNodes from BootnodesFlag

[buddh0]

bug description

conditions

1. BootstrapNodes is set in config.toml, no matter empty or not, like

[Node.P2P]
MaxPeers = 30
NoDiscovery = false
BootstrapNodes = []
StaticNodes = []
ListenAddr = ":30311"
EnableMsgEvents = false

2. start geth with flag BootnodesFlag

result

bootnode in BootnodesFlag is ignored

expected hehavior

reset the bootnode from BootnodesFlag

[rjl493456442]

The issue was introduced in this PR #25174, I think this PR is wrong is the first place.

But your fix is also not correct, it will reset the bootstrap nodes in the config file. I will suggest this approach.

// resolveBootstrapNodes resolves the URLs for configuring the bootstrap
// nodes. If the bootstrap nodes are already configured in the configuration
// file, they will only be overridden if the command line flag is specified.
func resolveBootstrapNodes(ctx *cli.Context, cfg *p2p.Config) []string {
	if cfg.BootstrapNodes != nil {
		return SplitAndTrim(ctx.String(BootnodesFlag.Name))
	}
	urls := params.MainnetBootnodes
	switch {
	case ctx.IsSet(BootnodesFlag.Name):
		urls = SplitAndTrim(ctx.String(BootnodesFlag.Name))
	case ctx.Bool(HoleskyFlag.Name):
		urls = params.HoleskyBootnodes
	case ctx.Bool(SepoliaFlag.Name):
		urls = params.SepoliaBootnodes
	case ctx.Bool(GoerliFlag.Name):
		urls = params.GoerliBootnodes
	}
	return urls
}

// setBootstrapNodes creates a list of bootstrap nodes from the command line
// flags, reverting to pre-configured ones if none have been specified.
func setBootstrapNodes(ctx *cli.Context, cfg *p2p.Config) {
	urls := resolveBootstrapNodes(ctx, cfg)
	if len(urls) == 0 {
		return
	}
	cfg.BootstrapNodes = make([]*enode.Node, 0, len(urls))
	for _, url := range urls {
		if url != "" {
			node, err := enode.Parse(enode.ValidSchemes, url)
			if err != nil {
				log.Crit("Bootstrap URL invalid", "enode", url, "err", err)
				continue
			}
			cfg.BootstrapNodes = append(cfg.BootstrapNodes, node)
		}
	}
}

[buddh0]

you are right, I'm agree with your approach.