face: move Channel and subclasses into nfd::face namespace

Change-Id: I163ef20e11b65d19d68585ec075fd3cd224a573b
diff --git a/daemon/face/ethernet-factory.cpp b/daemon/face/ethernet-factory.cpp
index fef7e96..cf0b34c 100644
--- a/daemon/face/ethernet-factory.cpp
+++ b/daemon/face/ethernet-factory.cpp
@@ -161,12 +161,12 @@
     return found->second;
   }
 
-  face::GenericLinkService::Options opts;
+  GenericLinkService::Options opts;
   opts.allowFragmentation = true;
   opts.allowReassembly = true;
 
-  auto linkService = make_unique<face::GenericLinkService>(opts);
-  auto transport = make_unique<face::MulticastEthernetTransport>(netif, address, m_mcastConfig.linkType);
+  auto linkService = make_unique<GenericLinkService>(opts);
+  auto transport = make_unique<MulticastEthernetTransport>(netif, address, m_mcastConfig.linkType);
   auto face = make_shared<Face>(std::move(linkService), std::move(transport));
 
   m_mcastFaces[key] = face;