malta: use as a default type device

malta: use as a default type device

There is currently no relevant definition for developerboard device type
in include/target.mk, thus packages like iptables, firewall, dnsmasq
etc. are missing in the default images, rendering it almost useless
for regular testing or normal use.

With this change, currently a default set of packages for "router" will
be installed to malta firmware images.

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@47325 3c298f89-4303-0410-b956-a3cf2f4a3e73