src: netlink: fix crash when ops doesn't support udata

src: netlink: fix crash when ops doesn't support udata

commit be737a1986bfee0ddea4bee7863dca0123a2bcbc upstream.

Whenever a new version adds udata support to an expression, then old
versions of nft will crash when trying to list such a ruleset generated
by a more recent version of nftables.

Fix this by falling back to 'type' format.

Fixes: 6e48df5329ea ('src: add "typeof" build/parse/print support')
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Pablo Neira Ayuso <pablo@netfilter.org>