Update ntttcp.py

Author: SRIKKANTH

lisa/tools/ntttcp.py

@@ -667,20 +667,28 @@ def send_ntttcp_udp_unified_perf_messages(
                 "relativity": MetricRelativity.LowerIsBetter,
                 "unit": "cycles/byte",
             },
-            {
-                "name": "server_mtu",
-                "value": int(server_mtu),
-                "relativity": MetricRelativity.NA,
-                "unit": "bytes",
-            },
-            {
-                "name": "client_mtu",
-                "value": int(client_mtu),
-                "relativity": MetricRelativity.NA,
-                "unit": "bytes",
-            },
         ]
 
+        # Only send MTU metrics if they are valid (not -1)
+        if client_mtu != -1:
+            metrics.append(
+                {
+                    "name": f"client_mtu{conn_suffix}",
+                    "value": int(client_mtu),
+                    "relativity": MetricRelativity.NA,
+                    "unit": "bytes",
+                }
+            )
+        if server_mtu != -1:
+            metrics.append(
+                {
+                    "name": f"server_mtu{conn_suffix}",
+                    "value": int(server_mtu),
+                    "relativity": MetricRelativity.NA,
+                    "unit": "bytes",
+                },
+            )
+
         self._send_unified_perf_metrics(
             metrics, test_case_name, test_result, TransportProtocol.Udp
         )