poke: change the short form of --freshness to -f

For consistency with ndnpingserver and ndnputchunks

Change-Id: I82afc6de29e207d65bf885b0acbabfc9da05a5a7
diff --git a/manpages/ndnpoke.rst b/manpages/ndnpoke.rst
index b5c105d..39af974 100644
--- a/manpages/ndnpoke.rst
+++ b/manpages/ndnpoke.rst
@@ -4,7 +4,7 @@
 Synopsis
 --------
 
-**ndnpoke** [-h] [-x *freshness*] [-F] [-S *info*] [-u\|\ -w *timeout*] [-v] [-V] *name*
+**ndnpoke** [-h] [-f *freshness*] [-F] [-S *info*] [-u\|\ -w *timeout*] [-v] [-V] *name*
 
 Description
 -----------
@@ -20,7 +20,7 @@
 ``-h, --help``
   Print help and exit.
 
-``-x, --freshness <freshness>``
+``-f, --freshness <freshness>``
   Set ``freshness`` (in milliseconds) as the ``FreshnessPeriod``.
 
 ``-F, --final``
diff --git a/tools/peek/ndnpoke/main.cpp b/tools/peek/ndnpoke/main.cpp
index 669ba2a..f2a6830 100644
--- a/tools/peek/ndnpoke/main.cpp
+++ b/tools/peek/ndnpoke/main.cpp
@@ -66,11 +66,11 @@
 
   po::options_description dataOptDesc("Data construction");
   dataOptDesc.add_options()
-    ("final,F",     po::bool_switch(&options.wantFinalBlockId),
-                    "set FinalBlockId to the last component of the Data name")
-    ("freshness,x", po::value<time::milliseconds::rep>()->default_value(options.freshnessPeriod.count()),
-                    "set FreshnessPeriod, in milliseconds")
-    ("signing-info,S",  po::value<std::string>(&signingStr), "see 'man ndnpoke' for usage")
+    ("freshness,f",    po::value<time::milliseconds::rep>()->default_value(options.freshnessPeriod.count()),
+                       "set FreshnessPeriod, in milliseconds")
+    ("final,F",        po::bool_switch(&options.wantFinalBlockId),
+                       "set FinalBlockId to the last component of the Data name")
+    ("signing-info,S", po::value<std::string>(&signingStr), "see 'man ndnpoke' for usage")
   ;
 
   po::options_description visibleOptDesc;