netfilter: nf_tables: support timeouts larger than 23 days

Marco De Benedetto says:
 I would like to use a timeout of 30 days for elements in a set but it
 seems there is a some kind of problem above 24d20h31m23s.

Fix this by using 'jiffies64' for timeout handling to get same behaviour
on 32 and 64bit systems.

nftables passes timeouts as u64 in milliseconds to the kernel,
but on kernel side we used a mixture of 'long' and jiffies conversions
rather than u64 and jiffies64.

Bugzilla: https://bugzilla.netfilter.org/show_bug.cgi?id=1237


Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>