netfilter: nf_tables: honor set timeout and garbage collection updates

[ Upstream commit 123b9961 ]

Set timeout and garbage collection interval updates are ignored on
updates. Add transaction to update global set element timeout and
garbage collection interval.

Fixes: 96518518 ("netfilter: add nftables")
Suggested-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>