Fix testRawQueryNXDomain in DnsResolverTest

This test can not pass in T-Mobile Network becauseT-Mobile
has configured their network to return a "search page" when
the user looks up a name that doesn't exist.
Enable private DNS before doing nxDomain test.

Bug: 144521720
Test: atest MultinetworkApiTest

(cherry picked from commit 5bffff7bf21bb197ac31b21b1db84337618ca107)

Change-Id: Iaa0e65813c4fb426d16f1a4a6e430d6501d68767
1 file changed