Communicate with BatteryStatsService through BatteryStatsManager

Mainline connectivity service is only allowed to use formal
APIs. Use new system API in BatteryStatsManager instead of
calling BatteryStatsService directly.

Bug: 171686421
Test: FrameworksNetTests
Change-Id: I1d1f0d2d456003e842ad77519667c0532995610d
Merged-In: I1d1f0d2d456003e842ad77519667c0532995610d