vendor.sh: add clarification to nogbe warning

if the user ran this on an x60 tarball, the no-gbe
warning seems confusing since that one has intel gbe,
but pre-ifd, so no gbe region in the flash; on pre-ifd
systems e.g. ich7 southbridge, the mac address was baked
into a separate gbe nvm on mask rom, inaccessible to users

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/vendor.sh

@@ -512,6 +512,8 @@ patch_release_roms()
 			    1>&2
 			printf "This board probably lacks Intel ethernet.\n" \
 			    1>&2
+			printf "(or it's pre-IFD Intel with Intel GbE NIC)\n" \
+			    1>&2
 		fi
 	fi