Nichestack Tutorial Using Arria V GX starter board

If memory serves, there is a function "get_mac_addr()" in the file "network_utilities.c" that gets generated with the simple socket server demo app. The names might be off from what I just said, but you ought to be able to find it just mucking around. It's probably trying to pull it from a (non-existent) flash, and you can just hardcode it to whatever you like.