security: Fix a bug in CommandInterestGenerator

In generate(), the unit of timestamp should milliseconds rather than nanoseconds.

Change-Id: I945635d635c66da53d4511b91108395fabb0650b
diff --git a/src/helper/command-interest-generator.cpp b/src/helper/command-interest-generator.cpp
index f08d524..c216680 100644
--- a/src/helper/command-interest-generator.cpp
+++ b/src/helper/command-interest-generator.cpp
@@ -22,7 +22,7 @@
 CommandInterestGenerator::generate(Interest& interest, 
 				   const Name& certificateName /*= DEFAULT_CERTIFICATE_NAME*/)
 {
-  int64_t timestamp = time::now();
+  int64_t timestamp = time::now() / 1000000;
   while(timestamp == m_lastTimestamp)
     {
       usleep(1000); //Guarantee unqiueness of timestamp