netfilter: nf_tables: release new hooks on unsupported flowtable flags

Release the list of new hooks that are pending to be registered in case
that unsupported flowtable flags are provided.

Fixes: 78d9f48f

 ("netfilter: nf_tables: add devices to existing flowtable")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>