Document more errno(s) on ADnsHelper_ API am: 96aa4824b9 am: 6d3d0879a3

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2899547

Change-Id: Ie40e2173d74ce07360ae3b468cb30cbbcc428139
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>