Use the new gerbil-libp2p library

[fare]

There is a gerbil-libp2p library, it depends on go-libp2p that was unmaintained at some point and is maintained again, but gerbil-libp2p might have bitrotted.

Someone else is creating a new gerbil-libp2p library, that we'll want to use eventually.

In the meantime, let's use some simple TCP server.

[p3rsik]

Update:
@fare said that the new gerbil-libp2p is on the way, for now we still need to add simple TCP server for these purposes