WD N600 & N750 image updates

Last night I made some changes to the build process of the generated images for the WD N600 and N750 routers.

Starting from r48362, the following changes are active:

1. The designated_driver_luci repository is enabled by default. This allows people to install luci by doing: opkg update && opkg install luci
2. Added an entry to /etc/opkg/distfeeds.conf that will point to that revisions base packages
3. Enabled building all KMODs for the openwrt kernel as packages. Combined with the above change, this allows auto-dependency resolution to work correctly.

As always, bug reports and comments are welcome.