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

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

Change-Id: I08cdb61d9eee5abe2988a1292be3617f342c6fdd
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>