if controlport is not defined, it depends on the controlhost value what the value should be
- if controlhost is the same as host (or if controlhost is not defined, so controlhost=host by default) : you can take port for the value of controlport
- if controlhost is different, you can't take the value of 'port' for 'controlport', because the host is not the same and you can't know that both ports will be the same, the best default in this case is the default mysql port.