Wifi turned on after reboot

I'm using my MacBook Pro (Retina, Mid 2012) mostly over Ethernet and therefore deactivated Wifi. But since El Capitan Wifi is activated after each boot/reboot. I then deactivate Wifi again (or even deleted and added the Wifi interface in the network settings), but Wifi gets activated after each boot/reboot. Very annoying.

This behavior already happened with 10.9 Mavericks, was solved with 10.10 Yosemite, and now appeared again with 10.11 El Capitan.

My actual workaround is a login-hook that disables Wifi:

sudo defaults write com.apple.loginwindow LoginHook '/Library/Application Support/LoginHook/wifi-off.sh'

wifi-off.sh contains:

#!/bin/bash

sudo -u username osascript -e 'networksetup -setairportpower en0 Off'