As evidenced here[1] the device MAC address can be stored at a random
offset in the hard_config partition. Rely on sysfs to update the MAC
address correctly.
Adjust config so that WAN is base MAC and LAN is base MAC +1 to better
match label and vendor OS.
[1] https://github.com/openwrt/openwrt/pull/2850#issuecomment-610809021
Signed-off-by: Thibaut VARÈNE <hacks@slashdirt.org>