Add a handler thread check to all public methods am: d5b24b4855 am: 0d95465152 am: 1c5f297a39

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

Change-Id: I250b95243ab3debacd785137685960edf566787a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>