security: use exponential backoff in CertificateFetcherFromNetwork

refs: #4718, #4712

Change-Id: I8def533528b82ea00096e9d87897acf31dff24a4
diff --git a/src/security/v2/certificate-fetcher-direct-fetch.cpp b/src/security/v2/certificate-fetcher-direct-fetch.cpp
index 0f240a2..a155dad 100644
--- a/src/security/v2/certificate-fetcher-direct-fetch.cpp
+++ b/src/security/v2/certificate-fetcher-direct-fetch.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2017 Regents of the University of California.
+ * Copyright (c) 2013-2018 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -53,7 +53,7 @@
     }
   }
   if (incomingFaceId != 0) {
-    Interest directInterest(keyRequest->m_interest);
+    Interest directInterest(keyRequest->interest);
     directInterest.refreshNonce();
     directInterest.setTag(make_shared<lp::NextHopFaceIdTag>(incomingFaceId));
     m_face.expressInterest(directInterest, nullptr, nullptr, nullptr);