Fix a bug where private DNS to v4-only servers don't validate.

Bug: 132670008
Test: Manual
Test: atest NetworkStackTests
Change-Id: I8ae6fa6f3800f5f6c9ee88ffe3b8ada34b96dee6
(cherry picked from commit aea0808d3b26dab24005afc39eb7ec4f4f333bae)
2 files changed