Add dtoverlay=pi3-disable-bt to /boot/config.txt. You need to be on the latest OSMC version for this to work.
Then run
sudo systemctl disable brcm43xx.service
Add dtoverlay=pi3-disable-bt to /boot/config.txt. You need to be on the latest OSMC version for this to work.
Then run
sudo systemctl disable brcm43xx.service