merge two onInterest callback into one

Change-Id: I82e8150239d795cb465ea2526624300590e4434c
diff --git a/src/ndncert-common.cpp b/src/ndncert-common.cpp
index 0a6c994..fc0e9c6 100644
--- a/src/ndncert-common.cpp
+++ b/src/ndncert-common.cpp
@@ -45,5 +45,22 @@
   }
 }
 
+std::string requestTypeToString(RequestType type)
+{
+  switch (type)
+  {
+  case RequestType::NEW:
+    return "New";
+  case RequestType::RENEW:
+    return "Renew";
+  case RequestType::REVOKE:
+    return "Revoke";
+  case RequestType::NOTINITIALIZED:
+    return "Not initalized";
+  default:
+    return "Unrecognized type";
+  }
+}
+
 }  // namespace ndncert
 }  // namespace ndn