add read timeout

[vinipsmaker]

This commit adds a set_read_timeout function similar to Rust's
set_read_timeout[1]. The differences compared to upstream are:

• Operation always succeed.
• It takes an i64 instead Duration.

[1] https://doc.rust-lang.org/nightly/std/net/struct.UdpSocket.html#method.set_read_timeout

[vinipsmaker]

PR updated/rebased

[vinipsmaker]

PR updated.

It's a lot more stable now.

[vinipsmaker]

On our usage of rust-utp, a stress test to study rust-utp was used and the failure rate was around 50%. With the new set-read-timeout, failure rate went to 0% (we already executed the test plenty of time and still no sign of failure). It's definitively more stable now.

[vinipsmaker]

We're still executing tests to find more problems within rust-utp and we found a few:

• inetic@1a578c6
• inetic@66e5b71
• inetic@a7b30f0
• ignore expected errors on Windows #24

All of them touches different parts of the code and show problems that are unrelated to this PR. I'd appreciate any input on this, as it's becoming a burden to maintain separate sets of patchsets. Merging just this one PR would already make things a tad easier, as it'd allow me to maintain the same set of changes to our code and to the upstream rust-utp, as this PR introduces a fundamental change in code.