Make header guards comply with Rule 3.2

refs: #3984

Change-Id: Iec7a0d9ff49cf6124af9e554432ee5f09a199651
diff --git a/nsync/sync-diff-leaf.h b/nsync/sync-diff-leaf.h
index 598a83e..eb16209 100644
--- a/nsync/sync-diff-leaf.h
+++ b/nsync/sync-diff-leaf.h
@@ -20,8 +20,8 @@
  *         Alexander Afanasyev <alexander.afanasyev@ucla.edu>
  */
 
-#ifndef SYNC_DIFF_LEAF_H
-#define SYNC_DIFF_LEAF_H
+#ifndef NLSR_NSYNC_SYNC_DIFF_LEAF_H
+#define NLSR_NSYNC_SYNC_DIFF_LEAF_H
 
 #include "sync-leaf.h"
 #include <boost/exception/all.hpp>
@@ -88,4 +88,4 @@
 
 } // Sync
 
-#endif // SYNC_DIFF_LEAF_H
+#endif // NLSR_NSYNC_SYNC_DIFF_LEAF_H