Print sendtime of messsages.

Change-Id: I42579bce6133a536df61da9355aed763a0b2e614
diff --git a/aos/build/queues/output/message_dec.rb b/aos/build/queues/output/message_dec.rb
index 20a0c9d..0f5694a 100644
--- a/aos/build/queues/output/message_dec.rb
+++ b/aos/build/queues/output/message_dec.rb
@@ -335,7 +335,7 @@
       args.push(["AOS_TIME_ARGS(static_cast<int32_t>(",
                  "::std::chrono::duration_cast<::std::chrono::seconds>(",
                  "#{parent}#{this_name}.time_since_epoch()).count()), ",
-                 "static_cast<int32_t>(::std::chrono::duration_cast<::std::chrono::nanoseconds>(",
+                 "static_cast<uint32_t>(::std::chrono::duration_cast<::std::chrono::nanoseconds>(",
                  "#{parent}#{this_name}.time_since_epoch() - ",
                  "::std::chrono::duration_cast<::std::chrono::seconds>(",
                  "#{parent}#{this_name}.time_since_epoch())).count()))"].join(''))