Do not poll on the port in `recv_timeout`

[flaper87]

Current implementation causes a wakeup every time it checks for new messages, which is very bad for the battery life among other things.

IRC Chat: https://botbot.me/mozilla/rust/msg/6023259/

[olsonjeffery]

tl;dr if we had #6842 this would be a non-issue.

[olsonjeffery]

so i dug in a bit and it looks like, maybe, #6842 is actually resolved? (there is std::select which punts the trait defintion to std::rt::select .. so I guess we would want to impl Select or whatever on uvio::UvTimer

@brson confirm/deny?

[alexcrichton]

I'm of the opinion that we shouldn't implement this polling strategy in the libraries at all. Without a short-term fix I don't think that this should be merged at all.

Polling is generally agreed upon as the wrong strategy, and I don't think that it's ok to expose these as core synchronization library functions when they will perform differently than you'd expect.

[alexcrichton]

Closing because #9194 wasn't merged.