face: use new-style async_accept API

Change-Id: Id9de72c0922ec9ea13e5b1d9ded27dd7edf67e38
diff --git a/daemon/face/unix-stream-channel.hpp b/daemon/face/unix-stream-channel.hpp
index 705d6f8..7c7f287 100644
--- a/daemon/face/unix-stream-channel.hpp
+++ b/daemon/face/unix-stream-channel.hpp
@@ -101,17 +101,11 @@
   accept(const FaceCreatedCallback& onFaceCreated,
          const FaceCreationFailedCallback& onAcceptFailed);
 
-  void
-  handleAccept(const boost::system::error_code& error,
-               const FaceCreatedCallback& onFaceCreated,
-               const FaceCreationFailedCallback& onAcceptFailed);
-
 private:
   const unix_stream::Endpoint m_endpoint;
+  const bool m_wantCongestionMarking;
   boost::asio::local::stream_protocol::acceptor m_acceptor;
-  boost::asio::local::stream_protocol::socket m_socket;
-  size_t m_size;
-  bool m_wantCongestionMarking;
+  size_t m_size = 0;
 };
 
 } // namespace nfd::face