Added the IsSendable (ushort) method

websocket-sharp/Ext.cs

@@ -610,6 +610,11 @@ namespace WebSocketSharp
              code == CloseStatusCode.TlsHandshakeFailure;
     }
 
+    internal static bool IsSendable (this ushort code)
+    {
+      return !code.IsReserved () || code.IsNoStatusCode ();
+    }
+
     internal static bool IsText (this string value)
     {
       var len = value.Length;