MINOR: flt-trace: Add an option to inhibits trace messages

The 'quiet' option may be set to inibits the trace messages. The trace filter is
a bit verbose. This option may be used to not display the messages.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 3ae4d5c..1d077fc 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -20272,6 +20272,7 @@
     <name>               is an arbitrary name that will be reported in
                          messages. If no name is provided, "TRACE" is used.
 
+    <quiet>              inhibits trace messages.
 
     <random-forwarding>  enables the random forwarding of parsed data. By
                          default, this filter forwards all previously parsed