logging: Add quiet option

Mostly for debug?
Sometimes logging changes timing.

src/nvt_log.c

@@ -15,6 +15,8 @@
 
 char            log_level = 0;
 
+static char     log_threshold = LOG_DEBUG;
+
 static FILE    *log_dest = NULL;
 
 void nvt_log_dest(int dest)
@@ -34,8 +36,10 @@ void nvt_log_dest(int dest)
     }
 }
 
-void nvt_log_level(int level)
+void nvt_log_level(int quiet, int level)
 {
+    if (quiet)
+        log_threshold = LOG_NOTICE;
     log_level = level;
 }
 
@@ -63,6 +67,9 @@ void nvt_log(int prio, const char *fmt, ...)
     const char     *eol;
     int             len;
 
+    if (prio > log_threshold)
+        return;
+
     va_start(arg, fmt);
     len = vsnprintf(buf, sizeof(buf), fmt, arg);