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

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

Change-Id: I14a83b3b24f9addfa8f9da8998950e270a415a70
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>