rule: json: fix wrong indentation in nft_rule_snprintf_json

Comestic cleanup.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
examples: nft-set-get: retrieve all sets per family

Likewise other nftables objects, this patch allows you to dump
the sets per family.

This is possible since kernel changes (netfilter: nf_tables: allow
to dump all existing sets), we can get the full list of sets per
family.

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