[automerger skipped] Register OnSubscriptionsChangedListener and cache results. am: 16800bf437 -s ours

am skip reason: Merged-In I889d4da725ccda713367309c257622a0bf9939f3 with SHA-1 c48d856976 is already in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/23720722

Change-Id: Ic91f3284a089e4d605025b24c80221c6bc11e228
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>