netfilter: nft_set_pipapo: call nft_trans_gc_queue_sync() in catchall GC

pipapo needs to enqueue GC transactions for catchall elements through
nft_trans_gc_queue_sync(). Add nft_trans_gc_catchall_sync() and
nft_trans_gc_catchall_async() to handle GC transaction queueing
accordingly.

Fixes: 5f68718b ("netfilter: nf_tables: GC transaction API to avoid race with control plane")
Fixes: f6c383b8 ("netfilter: nf_tables: adapt set backend to use GC transaction API")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>