Fix flaky testNoMetricsWrittenForShortDuration_LegacyApfFilter

Use dedicated mock Clocks for different ApfFilters to avoid possible
multi threads access to the mock object.

Bug: 315368147
Test: atest ConnectivityCoverageTests:android.net.apf.ApfTest# \
      testNoMetricsWrittenForShortDuration_LegacyApfFilter \
      --rerun-until-failure 500
Change-Id: Id227fc317c4e672efa6cea3f800976bf4603e7c9
2 files changed