iface-modem-3gpp: Check before registering
If the modem is already registered when ModemManager probes the modem, it will ignore the registration state since the modem is not enabled yet. Always querying the registration state before starting the registration procedure makes sure to catch such cases and not perform unnecessary registration steps.
Signed-off-by: Sven Schwermer sven.schwermer@disruptive-technologies.com