Set SO_REUSEPORT and remove port translation.

[dvc94ch]

So with this patch I was able to get ipfs-embed to traverse the nat in netsim-embed [0]. The outgoing port is hard coded to 31333 which is the port used by ipfs-embed by default. Since there may be multiple listeners it's unclear which port should be used for outgoing connections. Note that the example only works sometimes, other times it deadlocks and times out.

The first listener that works for the dialing address is used by the swarm when dialing. If no local_addr is provided the transport selects a suitable one.

• [0] https://github.com/ipfs-rust/netsim-embed/blob/master/examples/p2p.rs

[dvc94ch]

So this feature needs more work. While implementing a simple dial back protocol to test if nat traversal works I noticed that you need to disable port reuse when dialing, because otherwise it will fail. Any thoughts on how it should work?

Well we can retry without port reuse. The problem is if both parties try to open a connection at the same time, they'll both fail.

For the dial back protocol, since there already is an open connection the dial failed callback won't be called, so either a timeout is required or maybe a custom protocols handler. Not really sure how those work yet.

[dvc94ch]

@tomaka so what's the solution here? Wait for quic to land and use quick by default?