audit: export symbol for use with xt_AUDIT

When xt_AUDIT is built as a module, modpost reports a problem.

	MODPOST 322 modules
	ERROR: "audit_enabled" [net/netfilter/x_tables.ko] undefined!
	WARNING: modpost: Found 1 section mismatch(es).

Cc: Thomas Graf <tgraf@redhat.com>
Signed-off-by: Jan Engelhardt <jengelh@medozas.de>

kernel/audit.c

@@ -74,6 +74,8 @@ static int	audit_initialized;
 int		audit_enabled;
 int		audit_ever_enabled;
 
+EXPORT_SYMBOL_GPL(audit_enabled);
+
 /* Default state when kernel boots without any parameters. */
 static int	audit_default;