Add diagnostics on failure for PrivateDns test

IWLAN on U 24Q2 release may cause this test to fail, but this was
supposed to be addresed by CarrierConfigSetupTest already.

Add diagnostics on failure to figure out if the IWLAN config is as
expected.

Test: atest
Bug: 253698734
Change-Id: Iddc8975bb473979f9c2769cd178ef75644b82aa7
2 files changed