On the Poco X3 NFC the `vendor.bluetooth.soc` property is unset, and
instead it's the `vendor.qcom.bluetooth.soc` to be set to `cherokee`.

There might be more Qualcomm devices to use this property.

And indeed stop the search when powering off.

If the signal is very low and no station is found, scanning will never
stop.
So, detect when we have looped over, and stop scanning.

Fixes: #1

The Linux kernel documentation clearly states that the third parameter
of the ioctl helper macros is the type of the data being passed, not a
pointer to it. Passing a pointer not only causes all ioctls to have the
same data size, but, most importantly, makes it impossible to use the
same userspace code for 32 and 64 bits architectures.

This is especially a problem on devices (such as the BQ M10 tablets)
that use a 64-bit kernel and a 32-bit userspace.

Note to device maintainers: make sure that the fm_ioctl.h file in your
driver follows the same convention.

This test uses the cherokee backend because it's the only working
backend; but if we introduced a special backend for testing, we could do
without it.