netfilter: nf_tables: delete flowtable hooks via transaction list

Remove inactive bool field in nft_hook object that was introduced in
abadb2f8 ("netfilter: nf_tables: delete devices from flowtable").
Move stale flowtable hooks to transaction list instead.

Deleting twice the same device does not result in ENOENT.

Fixes: abadb2f8

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