Merge "Test: separate common methods to EthernetTetheringTestBase" am: a43bba1277 am: 3be769a343 am: a7fea98cae

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2319210

Change-Id: Ida2a4de9a0d30284e721a7b37c3adb065bc17ae0
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>