I thought that USB to Ethernet adapters where a universal thing and I was wrong. It took me a 517MB download to get to a 503kb .exe containing the drivers.
I downloaded the Boot Camp Support Software 5.1.5769 from https://support.apple.com/kb/DL1837?viewlocale=en_US&locale=en_US
If you extract the zip and go to the folder “BootCamp\Drivers\Asix” you will find the AsixSetup64.exe which is just 503kb.
Alternative: download the 503kb file from mega.
If it succeeds, it will show something similar to the picture below in the device manager