See Ludovic Ronsin's answer below about using dtoverlay, a method added in January 2017.

This post seems to be talking about this. The answer talks about disabling the drivers by editing the file /etc/modprobe.d/raspi-blacklist.conf and adding:

blacklist brcmfmac blacklist brcmutil 

Alternatively, you could use crontab -e and add:

@reboot sudo ifdown wlan0 

So that command runs at each boot.

Hope this helps, I'm still waiting for my Pi 3 to arrive.