broadband-modem-qmi: fix signal strength when built with --with-newest-qmi-commands

This patch fixes the signal strength values when using ModemManager built
with --with-newest-qmi-commands.

It was never getting a valid signal strength because the default (0) is
always greater than a valid signal strength, and the rssi_max handling
was completely wrong.

Signed-off-by: David McCullough <david.mccullough@accelecon.com>
broadband-modem-qmi: fix registration state when built with --with-newest-qmi-commands

This patch fixes the registration reporting/checking when ModemManager is
built with --with-newest-qmi-commands.  apply_cs and apply_ps were not
properly initialised and may never be true. Also fixes a CnP error for
mm_ps_registration_state.

Signed-off-by: David McCullough <david.mccullough@accelecon.com>
build: remove --with-newest-qmi-commands configure option

We don't want people to use the logic enabled by this switch, so remove it from
configure to avoid confusions. Developers can still enable the related code by
defining WITH_NEWEST_QMI_COMMANDS via CFLAGS; e.g.:

 $ NOCONFIGURE=1 ./autogen.sh
 $ ./configure CFLAGS="-DWITH_NEWEST_QMI_COMMANDS"
device: Don't loose track of devices as they are move 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.