Add tests in Ikev2VpnTest back to presubmit

Those tests are no longer flaky after fix being merged, so add
them back to presubmit.

Fix: 293239828
Test: atest CtsNetTestCases:android.net.cts.Ikev2VpnTest \
      --rerun-until-failure 100
Change-Id: I3e5b0f8053404b8840e8ce67ea82344ab53ce421
1 file changed