MINOR: cli: export cli_parse_default() definition in cli.h

Export the cli_parse_default() function in cli.h so it could be used in
other files.
diff --git a/include/proto/cli.h b/include/proto/cli.h
index b4cac0d..9ed2327 100644
--- a/include/proto/cli.h
+++ b/include/proto/cli.h
@@ -34,6 +34,8 @@
 
 int cli_has_level(struct appctx *appctx, int level);
 
+int cli_parse_default(char **args, char *payload, struct appctx *appctx, void *private);
+
 /* mworker proxy functions */
 
 int mworker_cli_proxy_create();