Fix maxdatalen option

Add the newline (\n) at the end of --maxdatalen option. Thus, the
usage menu is shown with all options at their own lines.

Also add the command's parameter and its default value on usage
menu.
Signed-off-by: Guilherme Maciel Ferreira <guilherme.maciel.ferreira@gmail.com>

src/samples/stdinpub.c

@@ -67,7 +67,7 @@ void usage()
 	printf("  --retained (default is off)\n");
 	printf("  --delimiter <delim> (default is \\n)\n");
 	printf("  --clientid <clientid> (default is stdin-publisher)\n");
-	printf("  --maxdatalen 100\n");
+	printf("  --maxdatalen <bytes> (default is 100)\n");
 	printf("  --username none\n");
 	printf("  --password none\n");
 	printf("  --keepalive <seconds> (default is 10 seconds)\n");

src/samples/stdinpuba.c

@@ -66,7 +66,7 @@ void usage()
 	printf("  --retained (default is off)\n");
 	printf("  --delimiter <delim> (default is \\n)\n");
 	printf("  --clientid <clientid> (default is stdin-publisher-async)\n");
-	printf("  --maxdatalen 100\n");
+	printf("  --maxdatalen <bytes> (default is 100)\n");
 	printf("  --username none\n");
 	printf("  --password none\n");
 	printf("  --keepalive <seconds> (default is 10 seconds)\n");