Test: Don't check the order of DNS answers in resolv_private_dns_test

Some tests are flaky because the order of answers is not expected.
For consistency with other tests, such as resolv_integration_test,
don't check the order of DNS answers.

Bug: 235965057
Test: atest
Change-Id: I3e6b04cce8034a2522fc8ccc35483551357b676d