Introduce network link quality statistics

This change starts tracking traffic quality data for WiFi and mobile
networks. The quality is tracked based on incidental traffic, and not
on specific measurements. Theoretical bandwidths are hard-coded, as
well as sampling interval; although sampling interval can be changed
by setting a system policy.

Bugs filed to remove shortcomings of this change -

10342372 Change LinkInfo name to something better
10342318 Move hardcoded values of MobileLinkInfo to resources
         so they can be updated without changing code

Bug: 10006249

Change-Id: I83d8c7594da20fe53abbd5e1f909b1f606b035bb