Disabling Bluetooth while booting?

[Arthur Chance]

I'm trying to install FBSD 11.1 amd64 on a 2015 HP Stream 13 using the
memstick image with UEFI booting. It boots OK and starts showing the
installer prompt, but then the screen is overwritten by non-stop console
messages reading

ubt0_intr_read_callback:878 interrupt transfer failed: USB_ERR_IOERROR

This is coming out of the ng_ubt code. What are the incantations I need
to disable this code? I can't find a device ubt line in the config file,
but I presume I need something like

ubt_load="NO"

in /boot/loader.conf or

hint.ubt.0.disabled="1"

in /boot/device.hints

Or are netgraph related devices different?

-- 
An amusing coincidence: log2(58) = 5.858 (to 0.0003% accuracy).