brcm63xx: provide a default sane MAC address for Cable Modem devices

Cable modem devices currently poke at some random location in RAM and
may end up having an invalid MAC address which is not suitable. Provide
a default one which is sane.

Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt@36957 3c298f89-4303-0410-b956-a3cf2f4a3e73
brcm63xx: refresh 3.9 patches

Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt@36958 3c298f89-4303-0410-b956-a3cf2f4a3e73