src: Allow list stateful objects in a table

src: Allow list stateful objects in a table

Currently, stateful objects can be listed by: listing all objects in
all tables; listing a single object in a table. Now it's allowed to
list all objects in a table.

$ nft list counters table filter
table ip filter {
	counter https-traffic {
		packets 14825 bytes 950063
	}
	counter http-traffic {
		packets 117 bytes 9340
	}
}

$ nft list quotas table filter
table ip filter {
	quota https-quota {
		25 mbytes used 2 mbytes
	}
	quota http-quota {
		25 mbytes used 10 kbytes
	}
}

Signed-off-by: Elise Lennion <elise.lennion@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>