Rust: discuss request-per-connection vs multiplexing

[brson]

The sync networking project leaves the protocol design entirely up to the student, but whether they choose to use a request per connection or multiple requests per connection has big implications once the project is converted to async.

Bring the topic up once during the networking project, then revisit during the async prjoect.

[brson]

Some discussion here https://pingcap.slack.com/archives/CF31LFWP7/p1559943113093100