Improve logger performance.

Source/MQTTnet.AspnetCore/MqttWebSocketServerAdapter.cs

@@ -10,15 +10,13 @@ using System.Threading.Tasks;
 
 namespace MQTTnet.AspNetCore
 {
-    public class MqttWebSocketServerAdapter : IMqttServerAdapter
+    public sealed class MqttWebSocketServerAdapter : IMqttServerAdapter
     {
-        private readonly IMqttNetLogger _logger;
+        readonly IMqttNetLogger _rootLogger;
 
         public MqttWebSocketServerAdapter(IMqttNetLogger logger)
         {
-            if (logger == null) throw new ArgumentNullException(nameof(logger));
-
-            _logger = logger.CreateChildLogger(nameof(MqttTcpServerAdapter));
+            _rootLogger = logger ?? throw new ArgumentNullException(nameof(logger));
         }
 
         public Func<IMqttChannelAdapter, Task> ClientHandler { get; set; }
@@ -51,7 +49,7 @@ namespace MQTTnet.AspNetCore
                     var formatter = new MqttPacketFormatterAdapter(writer);
                     var channel = new MqttWebSocketChannel(webSocket, endpoint, isSecureConnection, clientCertificate);
 
-                    using (var channelAdapter = new MqttChannelAdapter(channel, formatter, _logger.CreateChildLogger(nameof(MqttWebSocketServerAdapter))))
+                    using (var channelAdapter = new MqttChannelAdapter(channel, formatter, _rootLogger))
                     {
                         await clientHandler(channelAdapter).ConfigureAwait(false);
                     }