[Work in progress] Listen on TCP and publish ports over Upnp

[ikatson]

This is quite a big change. On Hacker News Rqbit post someone noted we don't upload which isn't great for the network.

I wondered what would it take to make this work without implementing uTP protocol.

So this change changes the default behavior of "rqbit server start" to work similar to other torrent clients - to upload by default.

Here's how it works:

• we start listening on TCP during session creation. You can turn it off with --disable-tcp-listen. There's also --tcp-listen-min(max)-port.
• we publish the local port over Upnp for port-forwarding on the router. You can disable it with --disable-upnp
• we pass this port to DHT when querying for peers, so that it starts announcing our address

The default listen port is 4240, it tries 20 more if it can't bind.

This actually works pretty well in the end, and the moment we publish on DHT, there's lots of peers who start connecting.

Also found bugs in upload code which recently broke, so in fact since some latest updates it likely wasn't uploading anything at all.

I was scratching my head on how to test this during dev, eventually just ran another client like this:

cargo run -- --disable-dht --disable-tcp-listen --disable-upnp --http-api-listen-addr 127.0.0.1:5000 download -o /tmp/scratch2 test.torrent --initial-peers 127.0.0.1:4240

So that one instance listens on 4240, and we force connect to it from another instance. This helped fix a couple bugs.