ar71xx: wndr4300: set official mac addresses

Get the factory assigned mac addresses stored in the caldata
partition and asign them to lan and wan interfaces. Also put
the correct mac addresses into the WiFi eeprom files to ensure
that the ath9k driver will use the correct ones.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Patchwork: http://patchwork.openwrt.org/patch/4350/
[juhosg:
  - move WiFi MAC address setup to the firmware hotplug file,
  - use the official MAC address for the 2.4GHz as well,
  - remove uci-defaults.sh modifications,
  - update commit message]
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38812 3c298f89-4303-0410-b956-a3cf2f4a3e73