DOC: config: Fix configuration example for mqtt
This patch fixes the example for mqtt_is_valid(), it was missing
curly braces within the ACL.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 442b61e..8724330 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -16513,7 +16513,7 @@
Example:
acl data_in_buffer req.len ge 4
- tcp-request content reject unless req.payload(0,0),mqtt_is_valid
+ tcp-request content reject unless { req.payload(0,0),mqtt_is_valid }
mul(<value>)
Multiplies the input value of type signed integer by <value>, and returns