malta: add default network configuration

I didn't figure out how to achieve this using uci-defaults-new.sh,
so use old-school uci-defaults script as that's what is used on
realview as well.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@45857 3c298f89-4303-0410-b956-a3cf2f4a3e73