selftests: netfilter: nft_concat_range.sh: add coverage for 4bit group representation

Pipapo supports a more compact '4 bit group' format that is chosen when
the memory needed for the default exceeds a threshold (2mb).

Add coverage for those code paths, the existing tests use small sets that
are handled by the default representation.

This comes with a test script run-time increase, but I think its ok:

 normal: 2m35s -> 3m9s
 debug:  3m24s -> 5m29s (with KSFT_MACHINE_SLOW=yes).

Cc: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>