netlink_delinearize: handle extension header templates with odd sizes

netlink_delinearize: handle extension header templates with odd sizes

This enables nft to display
	frag frag-off 33

... by considering a mask during binop postprocess in case
the initial template lookup done when the exthdr expression was
created did not yield a match.

In the above example, kernel netlink data specifies 16bits,
but the frag field is only 13bits wide.

We use the implicit binop mask to re-do the template lookup with
corrected offset and size information.

Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>