Use event pattern correctly for incoming server connections.

MQTTnet.Core/Server/MqttClientConnectedEventArgs.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace MQTTnet.Core.Server
+{
+    public class MqttClientConnectedEventArgs : EventArgs
+    {
+        public MqttClientConnectedEventArgs(ConnectedMqttClient client)
+        {
+            Client = client ?? throw new ArgumentNullException(nameof(client));
+        }
+
+        public ConnectedMqttClient Client { get; }
+    }
+}

MQTTnet.Core/Server/MqttClientDisconnectedEventArgs.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace MQTTnet.Core.Server
+{
+    public class MqttClientDisconnectedEventArgs : EventArgs
+    {
+        public MqttClientDisconnectedEventArgs(ConnectedMqttClient client)
+        {
+            Client = client ?? throw new ArgumentNullException(nameof(client));
+        }
+        
+        public ConnectedMqttClient Client { get; }
+    }
+}

MQTTnet.Core/Server/MqttServer.cs

@@ -77,9 +77,9 @@ namespace MQTTnet.Core.Server
             MqttNetTrace.Information(nameof(MqttServer), "Stopped.");
         }
 
-        private void OnClientAccepted(IMqttCommunicationAdapter adapter)
+        private void OnClientAccepted(object sender, MqttServerAdapterClientAcceptedEventArgs eventArgs)
         {
-            Task.Run(() =>_clientSessionsManager.RunClientSessionAsync(adapter), _cancellationTokenSource.Token);
+            Task.Run(() =>_clientSessionsManager.RunClientSessionAsync(eventArgs.Client), _cancellationTokenSource.Token);
         }
 
         private void OnClientConnected(object sender, MqttClientConnectedEventArgs eventArgs)