cache: include set elements in "nft set list"

cache: include set elements in "nft set list"

Make "nft list sets" include set elements in listing by default.
In nftables 1.0.0, "nft list sets" did not include the set elements,
but with "--json" they were included.

1.0.1 and newer never include them.
This causes a problem for people updating from 1.0.0 and relying
on the presence of the set elements.

Change nftables to always include the set elements.
The "--terse" option is honored to get the "no elements" behaviour.

Fixes: a1a6b0a5c3c4 ("cache: finer grain cache population for list commands")
Link: https://marc.info/?l=netfilter&m=168704941828372&w=2
Signed-off-by: Florian Westphal <fw@strlen.de>