API council feedbacks for DnsResolver

To address the API review feedback provided by
the API council.

Bug: 129261432
Test: atest DnsResolverTest

Merged-In: I5737cf293264bf9d492e7bd56b62bee4d49002eb
(cherry picked from commit 454fe010dcacd38211b857d2b235ed37269e3b7e)

Change-Id: I429dd93285f50314e9d757f4ec8539a3ba40e61b
5 files changed