[twamporch] Explicitly initialize local variable (#3115)

What I did
Explicitly initialized local variable.

Why I did it
We met below error message in sonic-buildimage armhf build (sonic-net/sonic-buildimage#18334)

orchagent/twamporch.cpp

@@ -690,6 +690,7 @@ task_process_status TwampOrch::createEntry(const string& key, const vector<Field
     if (entry.role == SAI_TWAMP_SESSION_ROLE_SENDER)
     {
         TwampStats hw_stats;
+        memset(&hw_stats, 0, sizeof(TwampStats));
         m_twampStatistics.emplace(key, hw_stats);
         initSessionStats(key);
     }