correct the link to the ddos article

Author: halkazwini

articles/route-server/TOC.yml

@@ -20,7 +20,7 @@
   - name: Peer Route Server with NVA
     href: tutorial-configure-route-server-with-quagga.md
   - name: Deploy Route Server with DDoS protection
-    href: tutorial-protect-route-server.md
+    href: tutorial-protect-route-server-ddos.md
 - name: Concepts
   items:
   - name: Route Server FAQ