Refactor server socket management for Linux support.

Frameworks/MQTTnet.NetStandard/Server/MqttServerTcpEndpointBaseOptions.cs

@@ -0,0 +1,17 @@
+using System.Net;
+
+namespace MQTTnet.Server
+{
+    public abstract class MqttServerTcpEndpointBaseOptions
+    {
+        public bool IsEnabled { get; set; }
+
+        public int Port { get; set; }
+
+        public int ConnectionBacklog { get; set; } = 10;
+
+        public IPAddress BoundInterNetworkAddress { get; set; } = IPAddress.Any;
+
+        public IPAddress BoundInterNetworkV6Address { get; set; } = IPAddress.IPv6Any;
+    }
+}