use the correct varnish 4 config

Author: dbu

resources/config/varnish-4/fos_custom_ttl.vcl

@@ -23,9 +23,9 @@ sub fos_custom_ttl_backend_response {
          * startup command.
          */
         C{
-            char *ttl;
-            ttl = VRT_GetHdr(sp, HDR_BERESP, "\024X-Reverse-Proxy-TTL:");
-            VRT_l_beresp_ttl(sp, atoi(ttl));
+            const struct gethdr_s hdr = { HDR_BERESP, "\024X-Reverse-Proxy-TTL:" };
+            ttl = VRT_GetHdr(ctx, &hdr);
+            VRT_l_beresp_ttl(ctx, atoi(ttl));
         }C
 
         unset beresp.http.X-Reverse-Proxy-TTL;