utils: eth_mac_addr: Refactor ethernet mac addr script am: e0b877ac38 am: 0ee1ffe493 am: 5bad9d4fe9

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

Change-Id: Ic0d8de87f2278ee3bcbf0faecc1039101dbed0d9
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>