Always wait for interface to be up in EthernetManagerTest am: 97631d8081

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/18513023

Change-Id: I87f07e75fbec8647eaa19ac32bfd37f415e7d329
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>