src: add comment support when adding tables

Adds userdata building logic if a comment is specified when creating a
new table. Adds netlink userdata parsing callback function.

Relies on kernel supporting userdata for nft_table.

Example:

> nft add table ip x { comment "test"\; }
> nft list ruleset

table ip x {
	comment "test"
}

Signed-off-by: Jose M. Guisado Gomez <guigom@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/rule.h b/include/rule.h
index 62d25be2..56f1951f 100644
--- a/include/rule.h
+++ b/include/rule.h
@@ -162,6 +162,7 @@ struct table {
 	struct list_head	chain_bindings;
 	enum table_flags 	flags;
 	unsigned int		refcnt;
+	const char		*comment;
 };
 
 extern struct table *table_alloc(void);