netfilter: nf_tables: restore notifications for anonymous set destruction

Since we have the context available again, we can restore notifications
for destruction of anonymous sets.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --cc net/netfilter/nf_tables_api.c
Simple merge

diff --cc net/netfilter/nft_lookup.c
Simple merge