socket stack, UDP listen (TCP as well) may result in EADDRINUSE

[hannesm]

The issue is that the OS may use some ports already, and our API (the port is passed to listen, which then bind is applied to) doesn't allow to "list the already used ports".

I've no good idea how to fix this, related is #292. Would be great to have a good API experience without exceptions popping up. Any ideas / suggestions?

[hannesm]

Since my use case is "a DNS resolver", where I don't really care about the specific UDP listening port -- I guess UNIX[tm] has the solution that you can bind with port = 0 (or no bind at all) and then thereafter getsockname. Now the question is whether we want the same for our UDP and TCP layers?