Merge "EthernetTetheringTest: join handler thread after calling quitSafely" am: 78fd43ec67 am: b2007796bb

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2485639

Change-Id: I1ff76ca12051f784c2acf6aa127d64f218dc68d2
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>