Repair two critical bug with Interest/NACK processing

- There was wrong selection of FIB face order in CcnxForwardingStrategy
- Stop reacting on NACK if there are no incoming faces (i.e., loop
  detected after interest is already satisfied)
diff --git a/model/ccnx-net-device-face.cc b/model/ccnx-net-device-face.cc
index dff7694..468d8f1 100644
--- a/model/ccnx-net-device-face.cc
+++ b/model/ccnx-net-device-face.cc
@@ -95,6 +95,7 @@
                                          const Address &to,
                                          NetDevice::PacketType packetType)
 {
+  NS_LOG_FUNCTION (device << p << protocol << from << to << packetType);
   Receive (p);
 }