Move battery stats to xt_qtaguid for data stats.

Replace TrafficStats calls by reading values from xt_qtaguid kernel
module. To keep BatteryStatsImpl changes lightweight, cache recently
parsed stats. Tracks mobile ifaces from ConnectivityService.

Refactor xt_qtaguid parsing into factory outside of NMS. Add stats
grouping based on UID, and total based on limiting filters like iface
prefix and UID.

Bug: 4902271
Change-Id: I533f116c434b77f93355bf95b839e7478528505b