face: Implementing new "isOnDemand" flag

This flags replaces isPermanent flag in datagram faces, but with the
reversed logic (isPermanent = !isOnDemand)

Change-Id: I37ba604e5f105ca95a79a08b8cfc3d640df8b412
Refs: #1376
diff --git a/daemon/face/udp-face.cpp b/daemon/face/udp-face.cpp
index d9ba1f3..7de4d34 100644
--- a/daemon/face/udp-face.cpp
+++ b/daemon/face/udp-face.cpp
@@ -11,10 +11,10 @@
 NFD_LOG_INCLASS_TEMPLATE_SPECIALIZATION_DEFINE(DatagramFace, UdpFace::protocol, "UdpFace");
 
 UdpFace::UdpFace(const shared_ptr<UdpFace::protocol::socket>& socket,
-                 bool isPermanent)
+                 bool isOnDemand)
   : DatagramFace<protocol>(FaceUri(socket->remote_endpoint()),
                            socket,
-                           isPermanent)
+                           isOnDemand)
 {
 }