Fix Log4J config example in docs (elastic#66386)

We lost the `logger.transport.name` line in elastic#65169 and I incorrectly
extrapolated from what was left and mangled it further in elastic#66318. This
commit fixes things.

docs/reference/setup/logging-config.asciidoc

@@ -179,7 +179,8 @@ This is most appropriate when debugging a problem on a single node.
 --
 [source,properties]
 ----
-logger.org.elasticsearch.discovery.level = debug
+logger.discovery.name = org.elasticsearch.discovery
+logger.discovery.level = debug
 ----
 
 This is most appropriate when you already need to change your Log4j 2