418792 - Session getProtocolVersion always returns null

+ Backporting just the getProtocolVersion from jetty 9.1

jetty-websocket/websocket-api/src/main/java/org/eclipse/jetty/websocket/api/UpgradeRequest.java

@@ -181,6 +181,16 @@ public class UpgradeRequest
     {
         return Collections.unmodifiableMap(parameters);
     }
+    
+    public String getProtocolVersion()
+    {
+        String version = getHeader("Sec-WebSocket-Version");
+        if (version == null)
+        {
+            return "13"; // Default
+        }
+        return version;
+    }
 
     public String getQueryString()
     {

jetty-websocket/websocket-api/src/main/java/org/eclipse/jetty/websocket/api/UpgradeResponse.java

@@ -163,7 +163,7 @@ public class UpgradeResponse
     /**
      * Set the list of extensions that are approved for use with this websocket.
      * <p>
-     * This is Advanced usage of the {@link WebSocketCreator} to allow for a custom set of negotiated extensions.
+     * This is Advanced usage of the WebSocketCreator to allow for a custom set of negotiated extensions.
      * <p>
      * Notes:
      * <ul>

jetty-websocket/websocket-common/src/main/java/org/eclipse/jetty/websocket/common/WebSocketSession.java

@@ -361,8 +361,6 @@ public class WebSocketSession extends ContainerLifeCycle implements Session, Inc
 
     /**
      * Open/Activate the session
-     * 
-     * @throws IOException
      */
     public void open()
     {
@@ -423,6 +421,7 @@ public class WebSocketSession extends ContainerLifeCycle implements Session, Inc
     public void setUpgradeRequest(UpgradeRequest request)
     {
         this.upgradeRequest = request;
+        this.protocolVersion = request.getProtocolVersion();
     }
 
     public void setUpgradeResponse(UpgradeResponse response)