Added minor unit test - the monolith of DatabaseDescriptor make it hard to add more.
The internode messaging refactor (CASSANDRA-15066) introduced a tiny regression to tracing. Previously CASSANDRA-13028 had changed the message emitted by traceOutgoingMessage to include the number of bytes.
"Sending %s message to %s"
"Sending %s message to %s message size %d bytes"
But the change was dropped during the refactor, it's easy to put it back.