Hi,
I also tried to get this running, but I had the same problem as juliannojungle.
But I recognized in some other thread, that "net-usb-KERNEL.tcz" has to be loaded and installed.
If I manually try to do "tce-load -i net-usb-KERNEL.tcz" eth0 appears and the module r8152 is loaded.
After a reboot, eth0 is gone again.
So I added the line "net-usb-KERNEL.tcz" in "/mnt/mmcblk0p2/tce/onboot.lst" instead of "net-usb-4.9.22-piCore.tcz".
After a reboot, it works!
Maybe you could try this also.
Best regards
Gerhard