add support for rotating among preferred network type

[gdt]

Generally, a phone is in LTE mode, and prefers LTE to 3G, and 3G to 2G. This is of course fine for actual use, but it results in not scanning 2G and 3G cellids in places with LTE coverage. One can manually set the phone to 3G and record those, or 2G, but that's not safe if driving.

This ticket asks for support in radiocells-nlp-android to change the data mode periodically. One approach is to change every few seconds, long enough to get a lock on the new mode and wait for it to settle. That might be bad for power use (even with external power, heat matters), and I don't know if each connection to data results in a charge (so perhaps an option to turn off mobile data when doing this?). But it might also result in signal strength measurements for cells in places where they are not the cell you end up on, which would be a bonus in the science project aspect. An alternative would be to change every 1 minute to 5 minutes. This would not necessarily scan all 3 modes on a given trip, but it would result in coverage over time without effort.

I don't know if apps can change this setting, or if the Settings app is special, etc.