Merge "Test: separate common methods to EthernetTetheringTestBase" am: a43bba1277

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

Change-Id: If094c40e9fb2fa1318ca3c7af89fcdad2ba480a6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>