device: Keep track of devices as they are move across sysfs

For certain devices the name changes with their status. Notably, RFCOMM
devices move from /devices/virtual/ to underneath the HCI that is used
for the connection as the session is estabilished, and return back when
it's torn down.
manager: Remove devices which are deemed unfit during addition attempt

device_added() might be called in response to a "change" or "move" attempt that
might have changed a candidate device to a non-candidate one.
udev: Don't mark disconnected RFCOMM ttys as candidates

Bluetooth serial devices are weird. They begin life being bound with
RFCOMMCREATEDEV ioctl() and then move around the sysfs tree when they are
connected and disconnected. The connection is estabilished upon the first
open() and torn down upon last close(), their first user virtually being
"owner" of the connection. We don't want to be that process, we're only
interested in actually connected modems. However, currently we have no
knowledge of that and therefore we connect and disconnect multiple times while
probing.

This patch marks unconnected RFCOMM devices as uninteresting to us.
The actual connection and disconnection will be handled by NetworkManager.