remove pseudo-device btdev(4) and inherent limitations
add bthub(4) which autoconfigures at bluetooth controllers as they
are enabled. bluetooth devices now attach here.
btdevctl(8) and its cache is updated to handle new semantics
etc/rc.d/btdevctl is updated to configure devices from a list
in /etc/bluetooth/btdevctl.conf
Remove bthset(4) device and add btsco(4) in its place. This is an
improved version which is not just for headsets, as it can receive
incoming connections (eg for Hands Free Profile). Update bthset(1)
control utlitiy to relate to new device.