demo: Fix missing record in mac demo

Will eventually become part of trashernet, I guess. But for now,
let's add it to the top level.

design/top_mac_test.vhd

@@ -52,6 +52,10 @@ architecture rtl of top_mac_test is
 		others     => false
 	);
 
+	type configuration_t is record
+		mac_address : mac_addr_t;
+	end record configuration_t;
+
 	constant ETH_CONFIG : configuration_t := (
 		mac_address => (x"00", x"ff", x"ff", x"11", x"22", x"33")
 	);