TCP_KEEPINTVL / TCP_KEEPCNT api missing

[aep]

mio::net::TcpStream::set_keepalive only lets you set TCP_KEEPIDLE, which isn't particularly useful.

resorting to nix::setsockopt over raw_fd works of course, but i suspect people will be confused, since the behavior when not setting TCP_KEEPINTVL is non-obvious, unless you know posix internals.

related tokio-rs/tokio-core#323

[carllerche]

Generally speaking, Mio tries to stick with a TCP API that mirrors std. Perhaps this issue should be filed on the rust-lang repo and as the API changes there, mio will follow.

[Thomasdezeeuw]

I agree with @carllerche and think we should stick to mirroring the API in the standard library, closing this. @aep I don't think getting this into the standard library will be that hard, UdpSocket::peer_addr also recently landed rust-lang/rust#59127.