Thanks @J-N-K and @rlkoshak for your replies!
I manged to adapt my script sending the battery status of my Windows tablet from UDP to writing it directly into the REST API of openHAB. So I can get rid of the TCP & UDP binding :-).
Another step into the direction of openHAB 3.X.
By the way, as textual configuration seems to be really outdated now, is there a way of “preparing” Things and Items in the UI, storing them and transferring their config? That I actually do with all my textual configuration. Besides my live openHAB 2.5 system, I have 3.x running for test purposes, try out step by step everything to find out where adaptations are needed and note or prepare them respectively in the configuration files. That allows me on a day X to switch from 2.x to 3.x and have it fully running within a short period of time (hopefully).
As by the new bindings, like the HTTP and TR-064, textual configuartion is not really foreseen anymore, I worry that it takes me a long time until I have everything setup properly over the UI.