ar71xx: use cybertan_check_image for image verification on the WRT160NL

That function provides a slightly improved sanity check than the
currently used solution.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

SVN-Revision: 38967

target/linux/ar71xx/base-files/lib/upgrade/platform.sh

@@ -171,7 +171,8 @@ platform_check_image() {
 		dir825b_check_image "$1" && return 0
 		;;
 
-	mynet-rext)
+	mynet-rext|\
+	wrt160nl)
 		cybertan_check_image "$1" && return 0
 		return 1
 		;;
@@ -275,13 +276,6 @@ platform_check_image() {
 		}
 		return 0
 		;;
-	wrt160nl)
-		[ "$magic" != "4e4c" ] && {
-			echo "Invalid image type."
-			return 1
-		}
-		return 0
-		;;
 	routerstation | \
 	routerstation-pro | \
 	ls-sr71 | \