Set wifi mac address during install.

This works in concert with a script we are adding to the device and injects the device specific mac address into the firmware, stored in the device's /persist partition and linked to from the system partition.

https://github.com/lbdroid/vendor_samsung_apexqtmo/blob/cc5cf84c897d422727ad5181a8f64519090452a8/proprietary/bin/wifimac.sh

This, obviously, requires no modification to d2-common, and doesn't rely on any boot-time hackery. The firmware is set once and persists.