[ndnSIM] face: Enable metric parameter on a face

Change-Id: I1de7298835af1fb329e356cbe74c3ac29fc53cea
diff --git a/daemon/face/face.cpp b/daemon/face/face.cpp
index 6422a39..b85cbb5 100644
--- a/daemon/face/face.cpp
+++ b/daemon/face/face.cpp
@@ -38,6 +38,7 @@
   , m_service(std::move(service))
   , m_transport(std::move(transport))
   , m_counters(m_service->getCounters(), m_transport->getCounters())
+  , m_metric(0)
 {
   m_service->setFaceAndTransport(*this, *m_transport);
   m_transport->setFaceAndLinkService(*this, *m_service);