src: Add additional log levels

refs: #1935

Change-Id: Ie3ef3f04fbcadd8fb9ee6f3aade4a35bd2a88105
diff --git a/nlsr.conf b/nlsr.conf
index 48f34a6..f204d12 100644
--- a/nlsr.conf
+++ b/nlsr.conf
@@ -14,9 +14,21 @@
   ; InterestLifetime (in seconds) for LSA fetching
   lsa-interest-lifetime 4    ; default value 4. Valid values 1-60
 
-  ; log-level is to set the levels of log for NLSR
+  ; log-level is used to set the logging level for NLSR.
+  ; All debugging levels listed above the selected value are enabled.
+  ;
+  ; Valid values:
+  ;
+  ;  NONE ; no messages
+  ;  ERROR ; error messages
+  ;  WARN ; warning messages
+  ;  INFO ; informational messages (default)
+  ;  DEBUG ; debugging messages
+  ;  TRACE ; trace messages (most verbose)
+  ;  ALL ; all messages
 
-  log-level  INFO       ; default value INFO, valid value DEBUG, INFO
+  log-level  INFO
+
   log-dir /var/log/nlsr/  ; path for log directory (Absolute path)
   seq-dir /var/lib/nlsr/  ; path for sequence directory (Absolute path)
 }