netfilter: nft_dynset: fix timeouts later than 23 days

Use nf_msecs_to_jiffies64 and nf_jiffies64_to_msecs as provided by
8e1102d5 ("netfilter: nf_tables: support timeouts larger than 23
days"), otherwise ruleset listing breaks.

Fixes: a8b1e36d ("netfilter: nft_dynset: fix element timeout for HZ != 1000")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>