GTP in previous kernels

Hi, I am currently working on building a GTP tunnel between two hosts. I used two virtual machines to implement GTP tunnel. The machines have the kernel 4.8 since GTP is in mainline. (I just did 'modprobe gtp') I setup the tunnel with libgtpnl tools. What I would like to do is that I want to have GTP module in a kernel 3.18. I did some google search and then I added the headers, libraries and the source code to the source code of 3.18 to compile all the kernel, but it didnt work. I am not experienced in kernel module programming or about the consequences compiling GTP in previous kernels which have different structural mechanisms than the 4.* versions. Is there any way to achieve this? If so, how could it be possible to get help from this community? Thanks all, Fırat