Mac driver for Lenovo L2230x Monitor
I guess you're chances are very small getting the monitor's Ethernet port working on OS X.
Probably you would need a modified kext - best place to ask would be the hackintosh sites - but you would have to be cautious with every OS X update as that could change the kext and leave you without working ethernet port...  

You could however use one of the USB ports on the monitor to connect the Apple USB Ethernet Adapter for ~30$ and you're save.  

You'd lose one USB port and 30 bucks, but I'd say it's better than the hacked solution over long time and you have an Ethernet adapter you can take with you, rather than carrying the monitor around ;)