netfilter: nft_payload: reject offsets exceeding 65535 bytes

netfilter: nft_payload: reject offsets exceeding 65535 bytes

Large offsets were rejected based on netlink policy, but blamed commit
removed the policy without updating nft_payload_inner_init() to use the
truncation-check helper.

Silent truncation is not a problem, but not wanted either, so add a
check.

Fixes: 077dc4a27579 ("netfilter: nft_payload: extend offset to 65535 bytes")
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>