Merge changes from topic "sp04"

* changes:
  [SP05] add unit test for onStatsProviderLimitReached in NPMS
  [SP04] add unit test for NetworkStatsProvider
  [SP03] support registerNetworkStatsProvider API
  [SP03.1] Replace com.android.internal.util.Preconditions.checkNotNull
tree: ca838059b046c6d63e60005aab80da137b0366b2
  1. core/
  2. packages/
  3. services/
  4. wifi/