Another approach:
I made two kernel images with the right dtb, please follow my description.
First, use this image again for prepare the SD card:
LibreELEC-MXIII-1G.arm-9.2.7.img.gz
Then download this, extract and overwrite the files on the card with these (kernel.img, kernel.img.md5, dtb.img):
LibreELEC-M8.arm-9.2.7-kernel.img+dtb.tar.gz
Then boot your box from this SD card and test the Ethernet.
If Ethernet still doesn't work, try this: