netfilter: x_tables: check name length in find_match/target, too

ebtables uses find_match() rather than find_request_match in one case
(see bcf49342

,
 "netfilter: ebtables: Fix extension lookup with identical name"), so
 extend the check on name length to those functions too.

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