netfilter: xtables: use xt_table for hook instantiation

The respective xt_table structures already have most of the metadata
needed for hook setup. Add a 'priority' field to struct xt_table so
that xt_hook_link() can be called with a reduced number of arguments.

So should we be having more tables in the future, it comes at no
static cost (only runtime, as before) - space saved:
6807373->6806555.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>

include/linux/netfilter/x_tables.h

@@ -361,6 +361,7 @@ struct xt_table {
 	struct module *me;
 
 	u_int8_t af;		/* address/protocol family */
+	int priority;		/* hook order */
 
 	/* A unique name... */
 	const char name[XT_TABLE_MAXNAMELEN];
@@ -522,6 +523,9 @@ static inline unsigned long ifname_compare_aligned(const char *_a,
 	return ret;
 }
 
+extern struct nf_hook_ops *xt_hook_link(const struct xt_table *, nf_hookfn *);
+extern void xt_hook_unlink(const struct xt_table *, struct nf_hook_ops *);
+
 #ifdef CONFIG_COMPAT
 #include <net/compat.h>