netfilter: nft_lookup: fix catchall element handling with inverted lookups

nft_lookup_eval() decides whether a lookup matched (`found`) from the
direct set lookup and priv->invert before falling back to the
catchall element used by interval sets (e.g. nft_set_rbtree) for the
open-ended default range. Since `found` is never recomputed after
`ext` is replaced by the catchall lookup, inverted lookups
(NFT_LOOKUP_F_INV, "!= @set") can wrongly match or wrongly skip the
catchall element, producing the wrong verdict. Fold the catchall
lookup into `ext` before computing `found`, matching the order
already used by nft_objref_map_eval().

Fixes: aaa31047a6d2 ("netfilter: nftables: add catch-all set element support")
Signed-off-by: Tamaki Yanagawa <ty@000ty.net>
Assisted-by: Claude:claude-sonnet-5
Signed-off-by: Florian Westphal <fw@strlen.de>