Export mdnsService struct or rename the Service interface for mDNS

[melroy89]

I would like to have my own struct, where I can assign mDNS service to mdns.NewMdnsService():

type MyStruct struct {
	mdnsService *mdns.mdnsService // Error: name mdnsService not exported by package  typesinternal#UnexportedName
}

// Meaning, this is currently NOT possible
MyStruct.mdnsService = mdns.NewMdnsService(p2pHost, "something", &mDNSNotifee{host: p2pHost})
if err := MyStruct.mdnsService.Start(); err != nil {
	panic(err)
} else {
	log.Println("mDNS service started")
}

If you would expose the mdns.mdnsService struct (just like you already do expose dht.IpfsDHT), I could assign it to my own struct.

Meaning it be much easier to later call a MyStruct.mdnsService.Close() on it for example. Maybe its just me, but I think it makes sense to export a struct that is getting returned by a public function.