No-op refactoring for TrafficStats APIs

Prepare for implementation of client side
TrafficStats rate limit cache.

1. Write Typeless versions of getIfaceStats,
getUidStats, getTotalStats in INetworkStatsService.aidl
that returns NetworkStats instead of Long.
This is needed because in follow-up changes,
the NetworkStats instead of indiviual numbers will
be stored as a cache entry

2. Move some utils from NetworkStatsService
to TrafficStats. This is needed because in the follow-up
changes, these utils would be both accessed by TrafficStats
and NetworkStatsService.

Test: CtsNetTestCases:android.net.cts.TrafficStatsTest
Test: CtsNetTestCases:android.net.cts.NetworkStatsBinderTest
Test: FrameworksNetIntegrationTests:com.android.server.net.\
		integrationtests.NetworkStatsIntegrationTest
Test: FrameworksNetTests:android.net.connectivity.com.android.\
		server.net.NetworkStatsServiceTest
Test: FrameworksNetTests:android.net.connectivity.\
		android.net.TrafficStatsTest
Test: ConnectivityCoverageTests:android.net.connectivity.\
	android.net.TrafficStatsTest
Bug: 343260158
Change-Id: Iace251e1495fd3b81e072526e92ca97cbc7246eb
5 files changed