People keep running into the same situation with newer hardware and we need to ask the same questions all the time.

1. Are you SURE you are using the latest kernel? Which version exactly?
2. What network adapter do you have? PCI IDs?
3. Is there some firmware missing your network card needs? Output of dmesg

Would be easy to add this information to the network script: https://github.com/FOGProject/fos/blob/master/Buildroot/board/FOG/FOS/rootfs_overlay/etc/init.d/S40network#L59