Remove TLS support for UWP servers because Framework does not support it.

MQTTnet.Core/Server/MqttServerTlsEndpointOptionsExtensions.cs

@@ -0,0 +1,19 @@
+using System;
+
+namespace MQTTnet.Core.Server
+{
+    public static class MqttServerTlsEndpointOptionsExtensions
+    {
+        public static int GetPort(this DefaultEndpointOptions options)
+        {
+            if (options == null) throw new ArgumentNullException(nameof(options));
+
+            if (!options.Port.HasValue)
+            {
+                return 1883;
+            }
+
+            return options.Port.Value;
+        }
+    }
+}