utils: eth_mac_addr: Refactor ethernet mac addr script am: e0b877ac38

Original change: https://android-review.googlesource.com/c/device/linaro/dragonboard/+/2664199

Change-Id: I393ef788434af4f7264560e437b0c6d8b91c6a2a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>