Fix the log level string of NONE.

include/ucore/logging.h

@@ -239,7 +239,7 @@ void uc_log_destination_set_module_loglevel(
  *  SHORT_NAME_1=LEVEL:SHORT_NAME_2=LEVEL:SHORT_NAME_N=LEVEL
  *
  * The SHORT_NAME_N is the .short_name within a struct uc_log_module
- * LEVEL is one of DEBUG,INFO, WARNING or ERROR
+ * LEVEL is one of DEBUG, INFO, WARNING, ERROR or NONE
  * Example: 
  *  DB=DEBUG:IO=ERROR:POLLER=INFO
  *

src/logging.c

@@ -75,6 +75,7 @@ static const char *const g_log_levels[] = {
     "WARNING",
     "UNKNOWN_6",
     "ERROR",
+    "UNKNOWN_8",
     "NONE"
 };