cache: chain listing implicitly sets on terse option

cache: chain listing implicitly sets on terse option

If user specifies a chain to be listed (which is internally handled via
filtering options), then toggle NFT_CACHE_TERSE to skip fetching set
content from kernel for non-anonymous sets.

With a large IPv6 set with bogons, before this patch:

 # time nft list chain inet raw x
 table inet raw {
        chain x {
                ip6 saddr @bogons6
                ip6 saddr { aaaa::, bbbb:: }
        }
 }

 real    0m2,913s
 user    0m1,345s
 sys     0m1,568s

After this patch:

 # time nft list chain inet raw prerouting
 table inet raw {
        chain x {
                ip6 saddr @bogons6
                ip6 saddr { aaaa::, bbbb:: }
        }
 }

 real    0m0,056s
 user    0m0,018s
 sys     0m0,039s

This speeds up chain listing in the presence of a large set.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>