Fix testUidTagStateDetails flaky by noise traffic

Query stats and create a baseline before actually testing
to prevent from test flaky caused by noise traffic.

Test: atest CtsNetTestCases:android.net.cts.NetworkStatsManagerTest \
      --rerun-until-failure 30
Fix: 368624224
Change-Id: I4cd29f98d46c40edffd513d53aa6299a8898275c
1 file changed