Add the vendor string, so it can be probed via AT commands. This allows
to support modems that are connected to a serial port.
Signed-off-by: Javier Viguera <javier.viguera@digi.com>
When the device is reset, it needs some time before the newly exposed TTYs are
able to reply to our AT commands. We increase the default timeout of the AT
probing commands in order to cope with that, or we'll end up with TTYs of
'unknown' type that aren't used for anything.