Sessions and Pre-Auth Commands
Certain MongoDB commands, like “ping” and “ismaster”, are processed outside of auth, and are used by drivers before authentication can begin. If a logical session id is passed to any of these commands, it will be ignored. Pre-auth commands cannot be associated with sessions.
When a driver runs one of these "pre-auth" commands with a session, the server ignores the session argument. We should document this behavior.
Document this for 4.2 and backport to 3.6 (once confirming the behavior is true through all major versions that support sessions)