selftests: nft_concat_range: Move option for 'list ruleset' before command

Before nftables commit fb9cea50e8b3 ("main: enforce options before
commands"), 'nft list ruleset -a' happened to work, but it's wrong
and won't work anymore. Replace it by 'nft -a list ruleset'.

Reported-by: Chen Yi <yiche@redhat.com>
Fixes: 611973c1 ("selftests: netfilter: Introduce tests for sets with range concatenation")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>