BLR: Improve disconnection reporting of connections via the MySQL interface

Maxscale logging shows in syslog after a disconnection from the binlog server's MySQL port:
Jun 25 17:34:00 xxxxx MaxScale[12049]: blr_service: Slave 1.2.3.4, server id 0, disconnected after 43 seconds. 0 events sent, 0 bytes.

I had actually sent some SQL commands to the binlog router, so it looks odd.

So the data shown are "binlog events", events and bytes.

Given that a SQL connection may be used for slave streaming or configuring the BLR it might be useful to adjust the logging:

Jun 25 17:34:00 xxxxx MaxScale[12049]: blr_service: Slave 1.2.3.4, server id 0, disconnected after 43 seconds. 999 SQL commands, 9999 binlog events (99999 bytes).