chunks+peek+ping: use correct underlying type for time::milliseconds

Change-Id: I3f46f846401eccc0c11d3abcd1a5ebff89056f7d
diff --git a/tools/peek/ndnpeek/ndnpeek.hpp b/tools/peek/ndnpeek/ndnpeek.hpp
index 0a9f503..d02155f 100644
--- a/tools/peek/ndnpeek/ndnpeek.hpp
+++ b/tools/peek/ndnpeek/ndnpeek.hpp
@@ -47,9 +47,9 @@
   bool canBePrefix = false;
   bool mustBeFresh = false;
   shared_ptr<Link> link;
-  optional<time::milliseconds> interestLifetime;
+  time::milliseconds interestLifetime = DEFAULT_INTEREST_LIFETIME;
 
-  // output behavior options
+  // program behavior options
   bool isVerbose = false;
   bool wantPayloadOnly = false;
   optional<time::milliseconds> timeout;