http2: implement ref() and unref() on client sessions

[mcollina]

• Version: master, 8.8.1
• Platform: all
• Subsystem: http2

Currently the client sessions cannot be unref(), which means they will keep the process alive if they are not destroyed. Adding support for ref() and unref() (https://nodejs.org/api/net.html#net_socket_ref) would add the possibility to create some long-running clients for the life of the process.

[mcollina]

cc @nodejs/http2

[addaleax]

So … a question; right now, this effectively is about the ref’edness of the uv_prepare_t that is used to send data at the beginning of an event loop iteration, and for the ref’edness of the underlying socket. Is that correct?

For the former, I think the solution we should be aiming for is to only have the handle be active if there actually is data to send, and I’d be glad to look into that.

[jasnell]

This has been done