swconfig: improve usability when switch device incorrect

http://patchwork.openwrt.org/patch/4701/

Signed-off-by: Andreas Mohr <andim2@users.sf.net>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39229 3c298f89-4303-0410-b956-a3cf2f4a3e73

cli.c

@@ -270,7 +270,7 @@ int main(int argc, char **argv)
 
 	dev = swlib_connect(cdev);
 	if (!dev) {
-		fprintf(stderr, "Failed to connect to the switch\n");
+		fprintf(stderr, "Failed to connect to the switch. Use the \"list\" command to see which switches are available.\n");
 		return 1;
 	}