sulu: disregard client-provided X-Forwarded-For

This prevents clients from lying about their identity to the MQTT
broker by supplying their own X-Forwarded-For in the request.

(cherry picked from commit 5631c28df4)

sulu/sulu-builder/files/etc/sulu/nginx.locations

@@ -20,7 +20,7 @@ location /wss {
 	proxy_set_header Connection $connection_upgrade;
 	proxy_set_header    Host               $host;
 	proxy_set_header    X-Real-IP          $remote_addr;
-	proxy_set_header    X-Forwarded-For    $proxy_add_x_forwarded_for;
+	proxy_set_header    X-Forwarded-For    $remote_addr;
 	proxy_set_header    X-Forwarded-Host   $host;
 	proxy_set_header    X-Forwarded-Server $host;
 	proxy_set_header    X-Forwarded-Port   $server_port;