Add a handler thread check to all public methods am: d5b24b4855 am: 0d95465152

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2593665

Change-Id: Iaf81018a192c4ecebe579039cd2ed778d6ede854
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>