Motivation:
TCP FastOpen is a pure optimisation, that is opportunistically applied.
There is no reason to make it specific to the epoll transport, and in the future we could add support to other transports.
Besides, the client-side equivalent, TCP_FASTOPEN_CONNECT, is already transport agnostic.
Modification:
Move the TCP_FASTOPEN channel option from EpollChannelOption to ChannelOption.
Mark the field in EpollChannelOption as deprecated.
Result:
All channel options related to TCP FastOpen are now transport agnostic.
However, we still only actually support TFO on the epoll transport.
32523c5337