Update C# bindings to 1.4.0 API

src/bindings/csharp/MulticastInfo.cs

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c)2013-2021 ZeroTier, Inc.
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file in the project's root directory.
+ *
+ * Change Date: 2026-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2.0 of the Apache License.
+ */
+/****/
+
+using System.Net;
+
+using ZeroTier;
+
+namespace ZeroTier.Core
+{
+    public class MulticastInfo {
+        public ulong MACAddress;
+        public uint additionalDistinguishingInformation;
+    }
+}