table: make FIB and StrategyChoice iterators default-constructible

They were previously not default-constructible when compiled with gcc 4.8.4.

refs #3882

Change-Id: I2431c869fb61b7adbe83d5551705981bf8618280
diff --git a/daemon/fw/face-table.cpp b/daemon/fw/face-table.cpp
index ed082bf..aaee894 100644
--- a/daemon/fw/face-table.cpp
+++ b/daemon/fw/face-table.cpp
@@ -25,12 +25,15 @@
 
 #include "face-table.hpp"
 #include "forwarder.hpp"
+#include "core/asserts.hpp"
 #include "core/global-io.hpp"
 #include "core/logger.hpp"
 #include "face/channel.hpp"
 
 namespace nfd {
 
+NFD_ASSERT_FORWARD_ITERATOR(FaceTable::const_iterator);
+
 NFD_LOG_INIT("FaceTable");
 
 FaceTable::FaceTable()