model: Huge bug with ndn::pit::Entry

Not setting PIT entry lifetime in the constructor resulted in immediate
removal of the PIT entries in some cases.  Reverting back behavior
changed by the previous commit.
diff --git a/model/pit/ndn-pit-entry.cc b/model/pit/ndn-pit-entry.cc
index 3847503..906fcdd 100644
--- a/model/pit/ndn-pit-entry.cc
+++ b/model/pit/ndn-pit-entry.cc
@@ -51,9 +51,9 @@
 
   // UpdateLifetime is (and should) be called from the forwarding strategy
 
-  // UpdateLifetime ((!header->GetInterestLifetime ().IsZero ()?
-  //                  header->GetInterestLifetime ():
-  //                  Seconds (1.0)));
+  UpdateLifetime ((!header->GetInterestLifetime ().IsZero ()?
+                   header->GetInterestLifetime ():
+                   Seconds (1.0)));
 }
 
 Entry::~Entry ()