Drop or reject lightweight connections

This is similar to haskell-distributed/distributed-process#434 but instead of dropping a bundle of connections to a peer, I'd like to be able to drop or reject one lightweight connection. This could be useful in case, for instance, a node is under heavy load and would like to continue to accept data on existing connections (perhaps some more data is needed) but reject new connections until the load is lessened.

Seems to me this would require a handshake when setting up lightweight connections. Currently if there's already a heavyweight connection to a peer then one simply sends a control code and then the connection is judged to be up and running, no response is expected. To allow rejection of the connection, the connector would have to wait for a yes or no response from the peer. Maybe this extra latency is unacceptable?

Start by reading the related haskell-distributed/distributed-process#434 issue and tracing the lightweight-connection setup and existing control-code handshake. Determine how a peer can accept or reject one new connection without dropping existing connections, and evaluate the latency concern. Done means the requested behavior is specified and implemented with coverage for acceptance and rejection.