[Feature Request] Allow setting custom protocol in mplex

[hanabi1224]

in go-libp2p-muxer, it allows using custom protocol name. Adding a similar pub fn set_protocol to MplexConfig to connect to go nodes with custom protocol.

// Muxer configures libp2p to use the given stream multiplexer (or stream
// multiplexer constructor).
//
// Name is the protocol name.
//
// The transport can be a constructed mux.Transport or a function taking any
// subset of this libp2p node's:
// * Peer ID
// * Host
// * Network
// * Peerstore
func Muxer(name string, tpt interface{}) Option {
	mtpt, err := config.MuxerConstructor(tpt)
	err = traceError(err, 1)
	return func(cfg *Config) error {
		if err != nil {
			return err
		}
		cfg.Muxers = append(cfg.Muxers, config.MsMuxC{MuxC: mtpt, ID: name})
		return nil
	}
}