lib: Add a helper function to dump Lua stack

Very handy for debugging.

In Lua script just use "log.trace(table)":

```
function on_rib_process_dplane_results(ctx)
	log.trace(ctx.rinfo.zd_ng)
end
```

You will get something like:

```
Aug 28 17:04:36 donatas-laptop zebra[3782199]: [GCZ7N-MM9D9] {
                                                 1: {
                                                   type: 2
                                                   weight: 1
                                                   flags: 5
                                                   backup_idx: 0
                                                   vrf_id: 0
                                                   nh_encap_type: 0
                                                   gate: {
                                                     value: 5.87967e+08
                                                     string: "192.168.11.35"
                                                   }
                                                   nh_label_type: 0
                                                   srte_color: 0
                                                   ifindex: 0
                                                   backup_num: 0
                                                 }
                                                 2: {
                                                   type: 3
                                                   weight: 1
                                                   flags: 3
                                                   backup_idx: 0
                                                   vrf_id: 0
                                                   nh_encap_type: 0
                                                   nh_label_type: 0
                                                   srte_color: 0
                                                   ifindex: 4
                                                   backup_num: 0
                                                 }
                                               }
```

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

1 files changed, 3 insertions, 0 deletions

diff --git a/lib/frrlua.h b/lib/frrlua.h
index dc0f4d9986..e407a4492f 100644
--- a/lib/frrlua.h
+++ b/lib/frrlua.h
@@ -181,6 +181,9 @@ int frrlua_table_get_integer(lua_State *L, const char *key);
  */
 void frrlua_export_logging(lua_State *L);
 
+/* A helper fuction that dumps the Lua stack */
+void lua_table_dump(lua_State *L, int index, struct buffer *buf, int level);
+
 /*
  * Dump Lua stack to a string.
  *