forward all refer to feature server

lib/call-session.js

@@ -783,11 +783,7 @@ class CallSession extends Emitter {
     try {
       const response = await dlg.other.request({
         method: 'REFER',
-        headers: {
-          'Refer-To': req.get('Refer-To'),
-          'Referred-By': req.get('Referred-By'),
-          'User-Agent': req.get('User-Agent')
-        }
+        headers: req.headers
       });
       res.send(response.status, response.reason);
     } catch (err) {