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

Change-Id: I4e0e44c62451629428d2d065692a0cb497a9203a
diff --git a/manpages/ndndump.rst b/manpages/ndndump.rst
index 51737bb..e219538 100644
--- a/manpages/ndndump.rst
+++ b/manpages/ndndump.rst
@@ -54,6 +54,10 @@
 
     Do not put the interface into promiscuous mode.
 
+.. option:: -t, --no-timestamp
+
+    Do not print a timestamp for each packet.
+
 .. option:: -v, --verbose
 
     Produce verbose output.