change SendQ data from variant to int64.

lichao

2021-05-14 34bc326eab06b9b1da2004a9e0d2182d63501d68

 utest/speed_test.cpp

@@ -57,7 +57,8 @@
      DEFER1(msg.Release(););

      for (uint64_t i = 0; i < n; ++i) {
         while (!mq.TrySend(id, msg)) {}
         msg.AddRef();
         while (!mq.TrySend(id, msg.Offset())) {}
         ++nwrite;
      }
   };