Set NFD logging level from GUI

refs: #2913

Change-Id: I4255b0467ef8ee6c4a2803ed078256cac9fbfd9c
diff --git a/ndn_utils/nfd.conf b/ndn_utils/nfd.conf
index ffb1f5c..246dc78 100644
--- a/ndn_utils/nfd.conf
+++ b/ndn_utils/nfd.conf
@@ -25,7 +25,7 @@
   ;  TRACE ; trace messages (most verbose)
   ;  ALL ; all messages
 
-  default_level NONE
+  default_level $LOG_LEVEL
 
   ; You may override default_level by assigning a logging level
   ; to the desired module name. Module names can be found in two ways: