Add more comments for the isConfigForIdentifiedCarrier()

This is a clean cherry-pick from:
https://android-review.git.corp.google.com/c/platform/frameworks/base/+/642231

Bug:74945742
Test: Compile
Change-Id: Ife3fdf797ca8877ec495d61a8aeed56fa20282a7
Merged-in: Ife3fdf797ca8877ec495d61a8aeed56fa20282a7
(cherry picked from commit cea0d8d4)