Fixup SntpClient to bypass Private DNS

NTP may be necessary in order to validate Private DNS certificates,
so it should be allowed to bypass Private DNS.

Test: as follows
    - built, flashed, booted
    - tcpdump for port 53; adb shell am restart
      queries for the NTP hostname appear in the clear
    - runtest frameworks-net passes
Bug: 64133961
Bug: 80118648
Change-Id: Id9ceb3fcaaffb48cbbd4cd381d48cae991572c9e