auditbeat - Add backlog_wait_time_actual to show-status

Now that go-libaudit support backlog_wait_time_actual this field
can be output from the show-status command on Linux 5.9+ kernels.

There were no tests for this code so I did a quick manual smoke test
on 5.10.

Relates elastic#31519

CHANGELOG.next.asciidoc

@@ -80,6 +80,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...main[Check the HEAD dif
 
 *Auditbeat*
 
+- Add `backlog_wait_time_actual` to the output of the `auditbeat auditd show-status` command. {pull}NNNN[NNNN]
 
 *Filebeat*
 

auditbeat/module/auditd/show_linux.go

@@ -123,6 +123,7 @@ func showAuditdStatus() error {
 		"lost %d%c"+
 		"backlog %d%c"+
 		"backlog_wait_time %d%c"+
+		"backlog_wait_time_actual %d%c"+
 		"features %s\n",
 		status.Enabled, separator,
 		status.Failure, separator,
@@ -132,6 +133,7 @@ func showAuditdStatus() error {
 		status.Lost, separator,
 		status.Backlog, separator,
 		status.BacklogWaitTime, separator,
+		status.BacklogWaitTimeActual, separator,
 		fmt.Sprintf("%#x", status.FeatureBitmap))
 
 	return nil