Add unit test for NetworkStatsSubscriptionsMonitor

Bug: 154080205
Test: atest FrameworksNetTests:com.android.server.net.NetworkStatsSubscriptionsMonitorTest
Change-Id: I4ef3f1ab2e5ea1322133edd80db3ccd0022e9c91
1 file changed
tree: 01bf84baf62c905611dc79f30f3cc88cc8a5c51f
  1. core/
  2. packages/
  3. services/
  4. wifi/