That sounds logical. There are a lot of ifdef in the Makefile referencing the 3.14 kernel. So that functions were probably declared in their 3.x header but not in the 4.x. To rule out this i'll apply the flag @neheb is pointing out to see were it takes me.
@philjohn yes, reading the code comments, Makefiles and doc there are a lot of references pointing out that the ecm (enhanced connection manager) is the module processing all the traffic rules and offloading.
So things are going slow but i'll try my best with the time i have for this task.
Thanks for the feedback ans tips!