Add testMobileDataPreferredUids back to presubmut

The testMobileDataPreferredUids was disabled from presubmit
because of flaky test. It's no longer flaky now, so add the test
back to presubmit.

Fix: 292174275
Test: atest android.net.cts.ConnectivityManagerTest\
      #testMobileDataPreferredUids --iterations 1000
Change-Id: I191888069a00942aa4c82f62bd1d62b7fc70b4fa