face: reimplement EndpointId with std::variant

Refs: #5041
Change-Id: Ib8aced49a7aa14b137fb06de4a0ae8b979f07587
diff --git a/tests/daemon/face/dummy-face.hpp b/tests/daemon/face/dummy-face.hpp
index 8374430..15ab445 100644
--- a/tests/daemon/face/dummy-face.hpp
+++ b/tests/daemon/face/dummy-face.hpp
@@ -60,17 +60,17 @@
   /** \brief causes the face to receive an Interest
    */
   void
-  receiveInterest(const Interest& interest, const EndpointId& endpointId);
+  receiveInterest(const Interest& interest, const EndpointId& endpointId = {});
 
   /** \brief causes the face to receive a Data
    */
   void
-  receiveData(const Data& data, const EndpointId& endpointId);
+  receiveData(const Data& data, const EndpointId& endpointId = {});
 
   /** \brief causes the face to receive a Nack
    */
   void
-  receiveNack(const lp::Nack& nack, const EndpointId& endpointId);
+  receiveNack(const lp::Nack& nack, const EndpointId& endpointId = {});
 
   /** \brief Emitted after a network-layer packet is sent.
    *