Fix service name in DynamicConfigurationManager

Author: andrewlock

tracer/src/Datadog.Trace/Configuration/DynamicConfigurationManager.cs

@@ -247,14 +247,12 @@ private ApplyDetails[] ConfigurationUpdated(
         private void ApplyMergedConfiguration(List<RemoteConfiguration> remoteConfigurations)
         {
             // Get current service/environment for filtering
-            var currentSettings = Tracer.Instance.Settings;
-            var serviceName = currentSettings.ServiceName;
-            var environment = currentSettings.Environment ?? Tracer.Instance.DefaultServiceName;
+            var currentSettings = Tracer.Instance.CurrentTraceSettings.Settings;
 
             var mergedConfigJToken = ApmTracingConfigMerger.MergeConfigurations(
                 remoteConfigurations,
-                serviceName,
-                environment);
+                serviceName: currentSettings.ServiceName,
+                environment: currentSettings.Environment);
 
             var configurationSource = new DynamicConfigConfigurationSource(mergedConfigJToken, ConfigurationOrigins.RemoteConfig);