model+helper+examples: Enable configurability of NFD parameters using StackHelper

Refs: #2353, #2220
diff --git a/helper/ndn-strategy-choice-helper.cpp b/helper/ndn-strategy-choice-helper.cpp
index 53e0209..53ba544 100644
--- a/helper/ndn-strategy-choice-helper.cpp
+++ b/helper/ndn-strategy-choice-helper.cpp
@@ -39,7 +39,7 @@
   commandName.append(encodedParameters);
 
   shared_ptr<Interest> command(make_shared<Interest>(commandName));
-  StackHelper::getKeyChain().signWithSha256(*command);
+  StackHelper::getKeyChain().sign(*command);
   Ptr<L3Protocol> L3protocol = node->GetObject<L3Protocol>();
   auto strategyChoiceManager = L3protocol->getStrategyChoiceManager();
   strategyChoiceManager->onStrategyChoiceRequest(*command);