apps: Enable congestion marking by default

Change-Id: Ib39d169b9765ed9270f59ca4770b1721772d1fc5
refs: #4672
diff --git a/helper/ndn-stack-helper.cpp b/helper/ndn-stack-helper.cpp
index 98bb186..82dab49 100644
--- a/helper/ndn-stack-helper.cpp
+++ b/helper/ndn-stack-helper.cpp
@@ -274,6 +274,7 @@
   ::nfd::face::GenericLinkService::Options opts;
   opts.allowFragmentation = true;
   opts.allowReassembly = true;
+  opts.allowCongestionMarking = true;
 
   auto linkService = make_unique<::nfd::face::GenericLinkService>(opts);
 
@@ -312,6 +313,7 @@
   ::nfd::face::GenericLinkService::Options opts;
   opts.allowFragmentation = true;
   opts.allowReassembly = true;
+  opts.allowCongestionMarking = true;
 
   auto linkService = make_unique<::nfd::face::GenericLinkService>(opts);