netfilter: nf_tables: skip bound chain in netns release path

Skip bound chain from netns release path, the rule that owns this chain
releases these objects.

Fixes: d0e2c7de ("netfilter: nf_tables: add NFT_CHAIN_BINDING")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Florian Westphal <fw@strlen.de>