Merge changes from topic "vpn_data_accounting" into qt-dev

* changes:
  Add one more test for VPN usage stats.
  Addressing comments for http://ag/7700679.
  NetworkStatsService: Fix getDetailedUidStats to take VPNs into account.
  Take all VPN underlying networks into account when migrating traffic for VPN uid.
tree: 1637a6bcbbc2e9630912e19ca7d0be342be9aaec
  1. core/
  2. services/
  3. tests/