dpdk: fix value is null exception

Author: LiliDeng

lisa/microsoft/testsuites/dpdk/dpdkperf.py

@@ -473,7 +473,7 @@ def _send_pps_unified_perf_messages(
                 test_case_name=test_case_name,
                 tool=tool,
                 metric_name=cast(str, metric["name"]),
-                metric_value=cast(float, metric["value"]),
+                metric_value=cast(float, metric.get("value", 0.0)),
                 metric_unit=cast(str, metric["unit"]),
                 metric_str_value=cast(str, metric.get("str_value", "")),
                 metric_relativity=cast(MetricRelativity, metric["relativity"]),