lib: Load built-in Lua functions

We can't use even `string()` function because built-in functions are not
loaded.

Testing with:

```
$ cat /etc/frr/scripts/zebra.lua
function on_rib_process_dplane_results(ctx)
	log.warn(string.upper("testas"))
	return {}
end
```

This results to "TESTAS" in the logs.

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/lib/frrscript.c b/lib/frrscript.c
index acdd1df67b..dbae31b666 100644
--- a/lib/frrscript.c
+++ b/lib/frrscript.c
@@ -348,6 +348,9 @@ int frrscript_load(struct frrscript *fs, const char *function_name,
 	/* Set up the Lua script */
 	lua_State *L = luaL_newstate();
 
+	/* Load basic built-in Lua functions, e.g. ipairs, string, etc. */
+	luaL_openlibs(L);
+
 	frrlua_export_logging(L);
 
 	char script_name[MAXPATHLEN];