Is there a public interface for controlling the connection limit on servers
created with `loop.create_server`? Specifically a way to ~
I've developed a statsd proxy for a client that needs to implement
backpressure all the way to the listening socket but I don't see a good way
to pause the _accept_connection handler that monitors the listening socket
for read events.
I'd be happy to implement my own logic for the back pressure using a public
`pause_serving()`/`resume_serving()` API but a simple `max_connections`
param to the create_server would suffice too.