Add a PersistentInt class. am: 2ce66fc8e6

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2103106

Change-Id: I3459550d61458fcb60cc7269e6462867ea97e0a6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>