Fix incorrect WebSocket close status description (#3294)

Author: castholm

xml/System.Net.WebSockets/WebSocketCloseStatus.xml

@@ -122,7 +122,7 @@
       </ReturnValue>
       <MemberValue>1011</MemberValue>
       <Docs>
-        <summary>The connection will be closed by the server because of an error on the server.</summary>
+        <summary>(1011) The connection will be closed by the server because of an error on the server.</summary>
       </Docs>
     </Member>
     <Member MemberName="InvalidMessageType">
@@ -250,7 +250,7 @@
       </ReturnValue>
       <MemberValue>1009</MemberValue>
       <Docs>
-        <summary>(1004) Reserved for future use.</summary>
+        <summary>(1009) The client or server is terminating the connection because it has received a message that is too big for it to process.</summary>
       </Docs>
     </Member>
     <Member MemberName="NormalClosure">