face: move isListening()/size() to Channel as pure virtual methods

As a side effect, this ensures that Channel cannot be instantiated.

Change-Id: I875876ddf8fc0fbb04f3e88726c708ece8106702
diff --git a/tests/daemon/face/unix-stream-channel.t.cpp b/tests/daemon/face/unix-stream-channel.t.cpp
index 1a356c0..c602f97 100644
--- a/tests/daemon/face/unix-stream-channel.t.cpp
+++ b/tests/daemon/face/unix-stream-channel.t.cpp
@@ -103,13 +103,13 @@
   this->listen();
 
   BOOST_CHECK_EQUAL(listenerChannel->isListening(), true);
-  BOOST_CHECK_EQUAL(listenerFaces.size(), 0);
+  BOOST_CHECK_EQUAL(listenerChannel->size(), 0);
 
   local::stream_protocol::socket client1(g_io);
   this->clientConnect(client1);
 
   BOOST_CHECK_EQUAL(limitedIo.run(2, time::seconds(1)), LimitedIo::EXCEED_OPS);
-  BOOST_CHECK_EQUAL(listenerFaces.size(), 1);
+  BOOST_CHECK_EQUAL(listenerChannel->size(), 1);
 
   local::stream_protocol::socket client2(g_io);
   local::stream_protocol::socket client3(g_io);
@@ -117,6 +117,7 @@
   this->clientConnect(client3);
 
   BOOST_CHECK_EQUAL(limitedIo.run(4, time::seconds(1)), LimitedIo::EXCEED_OPS);
+  BOOST_CHECK_EQUAL(listenerChannel->size(), 3);
   BOOST_CHECK_EQUAL(listenerFaces.size(), 3);
 
   // check face persistency
diff --git a/tests/daemon/mgmt/face-manager.t.cpp b/tests/daemon/mgmt/face-manager.t.cpp
index 8856b0a..41dcb90 100644
--- a/tests/daemon/mgmt/face-manager.t.cpp
+++ b/tests/daemon/mgmt/face-manager.t.cpp
@@ -247,6 +247,18 @@
   {
     setUri(FaceUri(uri));
   }
+
+  bool
+  isListening() const final
+  {
+    return false;
+  }
+
+  size_t
+  size() const final
+  {
+    return 0;
+  }
 };
 
 class TestProtocolFactory : public face::ProtocolFactory