Add Cellular panel to manage modems
The panel supports 2G/3G/4G GSM/LTE modems. CDMA2000 Modems are not supported. If a supported modem is present, the panel will be shown and the modem will be handled, else, network-panel shall manage the modem as it did in the past.
If more than one modem with data enabled is present, the user is allowed to use priority of one SIM over the other (the priority is for SIM, not modem).
As many CDMA2000/EVDO networks are being shutting down[0], I don't know if we need to actually support those modems. My country (India) no longer have any such networks. So I couldn't test such a modem.