dump: add -t option to suppress printing per-packet timestamp

Change-Id: I4e0e44c62451629428d2d065692a0cb497a9203a
diff --git a/tools/dump/ndndump.cpp b/tools/dump/ndndump.cpp
index 4c43826..77743a8 100644
--- a/tools/dump/ndndump.cpp
+++ b/tools/dump/ndndump.cpp
@@ -158,7 +158,9 @@
   }
 
   std::ostringstream os;
-  printTimestamp(os, pkthdr->ts);
+  if (wantTimestamp) {
+    printTimestamp(os, pkthdr->ts);
+  }
 
   ssize_t payloadSize = pkthdr->len;