This worklog adds capability to specify a separate IP address and TCP port
that are ready to accept TCP connection and speak MySQL protocol.
The following features are added within the worklog:

  * The new command-line options --admin-address and --admin-port
    to specify admin interface for listening incoming connection requests.

  * The new privilege SERVICE_CONNECTION_ADMIN to restrict
    access to admin socket.

  * Ignore restrictions imposed by parameters max_user_connections
    and max_connections in case a connection is made to admin interface.

  * The new option --create-admin-listener-thread to listen on admin interface
    in a separate thread.