added back MqttTrace consuming api

Frameworks/MQTTnet.NetStandard/MqttFactory.cs

@@ -18,11 +18,16 @@ namespace MQTTnet
 
         private static IServiceProvider BuildServiceProvider()
         {
-            return new ServiceCollection()
+            var serviceProvider =  new ServiceCollection()
                 .AddMqttClient()
                 .AddMqttServer()
                 .AddLogging()
                 .BuildServiceProvider();
+
+            serviceProvider.GetRequiredService<ILoggerFactory>()
+                .AddMqttTrace();
+
+            return serviceProvider;
         }
 
         public MqttFactory()

Frameworks/MQTTnet.NetStandard/ServiceCollectionExtensions.cs

@@ -6,6 +6,8 @@ using MQTTnet.Core.Serializer;
 using MQTTnet.Core.Server;
 using MQTTnet.Implementations;
 using System;
+using Microsoft.Extensions.Logging;
+using MQTTnet.Core.Diagnostics;
 
 namespace MQTTnet
 {
@@ -27,7 +29,6 @@ namespace MQTTnet
 
             services.AddTransient<MqttClientSessionsManager>();
             services.AddTransient<MqttClientRetainedMessagesManager>();
-
             return services;
         }
 
@@ -51,5 +52,11 @@ namespace MQTTnet
 
             return services;
         }
+
+        public static ILoggerFactory AddMqttTrace(this ILoggerFactory factory)
+        {
+            factory.AddProvider(new MqttNetTrace());
+            return factory;
+        }
     }
 }