Merge changes from topic "dscp-cts13-r2" into android13-tests-dev

* changes:
  DscpPolicy: remove v6 default route as it is added by the RA
  deflake DscpPolicyTest
  Update DscpPolicyTest to use random IPv6 prefixes.
  DscpPolicyTest: annotate with ConnectivityModuleTest
  DscpPolicy BPF Add Checksum Validation to Test
  DscpPolicyTest: fix linter errors