Add more unit test for doh

Test: atest doh_unit_test
Bug: 155855709

Original change: https://android-review.googlesource.com/c/platform/packages/modules/DnsResolver/+/1676245

Change-Id: Idf0a7f695c877bc5818ab5fc81133d35a38925dc
Merged-In: Idf0a7f695c877bc5818ab5fc81133d35a38925dc
(cherry picked from commit 36a05f5a)
Ignore-AOSP-First: To solve the confict between mainline-prod and other branches with newer toolchain.