netfilter: nf_tables: fix kdoc warnings after gc rework

Jakub Kicinski says:
  We've got some new kdoc warnings here:
  net/netfilter/nft_set_pipapo.c:1557: warning: Function parameter or member '_set' not described in 'pipapo_gc'
  net/netfilter/nft_set_pipapo.c:1557: warning: Excess function parameter 'set' description in 'pipapo_gc'
  include/net/netfilter/nf_tables.h:577: warning: Function parameter or member 'dead' not described in 'nft_set'

Fixes: 5f68718b ("netfilter: nf_tables: GC transaction API to avoid race with control plane")
Fixes: f6c383b8 ("netfilter: nf_tables: adapt set backend to use GC transaction API")
Reported-by: Jakub Kicinski <kuba@kernel.org>
Closes: https://lore.kernel.org/netdev/20230810104638.746e46f1@kernel.org/Signed-off-by: Florian Westphal <fw@strlen.de>

include/net/netfilter/nf_tables.h

@@ -534,6 +534,7 @@ struct nft_set_elem_expr {
  *	@expr: stateful expression
  * 	@ops: set ops
  * 	@flags: set flags
+ *	@dead: set will be freed, never cleared
  *	@genmask: generation mask
  * 	@klen: key length
  * 	@dlen: data length

net/netfilter/nft_set_pipapo.c

@@ -1549,7 +1549,7 @@ static void nft_pipapo_gc_deactivate(struct net *net, struct nft_set *set,
 
 /**
  * pipapo_gc() - Drop expired entries from set, destroy start and end elements
- * @set:	nftables API set representation
+ * @_set:	nftables API set representation
  * @m:		Matching data
  */
 static void pipapo_gc(const struct nft_set *_set, struct nft_pipapo_match *m)