“If you have access to a system that wasn’t updated with Ethernet Killer:
Go to System/Library/Extensions/AppleKextExcludeList.kext and copy the working file extension and transfer the file over to your corrupted computer or partition
Turn off System Integrity Protection (SIP) by restarting in recovery mode (command-R) and go under Utility in the top menu and open Terminal app.
Type in “csrutil disable” and return.
Restart computer and you now with be able to delete the bad
AppleKextExcludeList.kext and drop in the good AppleKextExcludeList.kext
Restart and Ethernet will be recognized again.
Turn the SIP back on by doing step 2 and 3 again but type in “csrutil enable”
Update: Apple has published the official fix in this support document.