Update docs.asciidoc (elastic#11852)

* Update docs.asciidoc

Added in a short note on a few of the other configurable variables.

* Make update

Author: markwalkom

filebeat/docs/modules/iptables.asciidoc

@@ -67,6 +67,17 @@ include::../include/config-option-intro.asciidoc[]
 
 include::../include/var-paths.asciidoc[]
 
+*`var.syslog_host`*::
+
+The interface to listen to UDP based syslog traffic. Defaults to `localhost`.
+Set to `0.0.0.0` to bind to all available interfaces.
+
+*`var.syslog_port`*::
+
+The UDP port to listen for syslog traffic. Defaults to `9001`
+
+NOTE: Ports below 1024 require Filebeat to run as root.
+
 :has-dashboards!:
 
 :fileset_ex!:

x-pack/filebeat/module/iptables/_meta/docs.asciidoc

@@ -62,6 +62,17 @@ include::../include/config-option-intro.asciidoc[]
 
 include::../include/var-paths.asciidoc[]
 
+*`var.syslog_host`*::
+
+The interface to listen to UDP based syslog traffic. Defaults to `localhost`.
+Set to `0.0.0.0` to bind to all available interfaces.
+
+*`var.syslog_port`*::
+
+The UDP port to listen for syslog traffic. Defaults to `9001`
+
+NOTE: Ports below 1024 require Filebeat to run as root.
+
 :has-dashboards!:
 
 :fileset_ex!: