ipq806x: nbg6817: sync MAC addresses to the upstream values

ipq806x: nbg6817: sync MAC addresses to the upstream values

The ZyXEL NBG6817 calculates all MAC addresses based on the ethaddr
value stored in the U-Boot environment (0:APPSBLENV). No MAC addresses
are stored in the ART partition and the generated MAC addresses for the
wlan interfaces alternate randomly between 12:34:56:78:90:12 and
00:03:7f:12:34:56.

interface	  new/ OEM MAC	old MAC

wlan-2.4g (phy1): ethaddr	undefined
wlan-5g   (phy0): ethaddr + 1	undefined
lan             : ethaddr + 2	ethaddr
wan             : ethaddr + 3	ethaddr + 1

This patch defines stable MAC addresses for the wlan interfaces for
the first time instead of generating them at random. The previously
defined values for lan/ wan are changed to follow the settings of the
OEM firmware.

Signed-off-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>