add missing #include

sscanf requires stdio.h
fixes commit open-mpi/ompi@6ca57724c4

opal/util/net.c

@@ -13,6 +13,8 @@
  *                         reserved. 
  * Copyright (c) 2009-2015 Cisco Systems, Inc.  All rights reserved.
  * Copyright (c) 2013      Intel, Inc.  All rights reserved.
+ * Copyright (c) 2015      Research Organization for Information Science
+ *                         and Technology (RIST). All rights reserved.
  * $COPYRIGHT$
  * 
  * Additional copyrights may follow
@@ -22,6 +24,7 @@
 
 #include "opal_config.h"
 
+#include <stdio.h>
 #include <string.h>
 #ifdef HAVE_UNISTD_H
 #include <unistd.h>