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/tests/face/ethernet.cpp b/tests/face/ethernet.cpp
index 2e731bf..4859da2 100644
--- a/tests/face/ethernet.cpp
+++ b/tests/face/ethernet.cpp
@@ -74,6 +74,8 @@
     factory.createMulticastFace(interfaces[0], ethernet::getDefaultMulticastAddress());
 
   BOOST_REQUIRE(static_cast<bool>(face));
+
+  BOOST_CHECK(!face->isOnDemand());
   BOOST_CHECK_EQUAL(face->isLocal(), false);
   BOOST_CHECK_EQUAL(face->getUri().toString(),
                     "ether://" + interfaces[0] + "/" +