Refactor shouldTestThisNetworkType

This is a no-op refactoring for test.

Currently, shouldTestThisNetworkType method check test
preconditions and generating network traffic for testing.
Decouple these two functionalities to allow follow-up
changes to capture data usage baseline prior to
generating network traffic.

Test: atest CtsNetTestCases:android.net.cts.NetworkStatsManagerTest \
      --rerun-until-failure 30
Bug: 368624224
Change-Id: I5510184ec0cf8afa05b46f78ebaf80e500abaeeb
1 file changed