Support for TCP Fastopen

[zerodefect]

I came across this article, so I'm now curious about TCP Fastopen support when 'Simple Web Server' (SWS) is used on Linux:

1. Is TCP Fastopen currently supported by SWS?
2. Are code changes required in SWS to support TCP Fastopen or can it work 'straight out the box'?
3. Is the Boost library capable of using TCP Fastopen?

[eidheim]

Without looking too closely on this, you can maybe use native_handle as shown here: https://stackoverflow.com/a/44308194. We could maybe add an option for this, but it would require a pull request for someone wanting to look into this:)