selftests: netfilter: nft_concat_range.sh: add datapath check for map fill bug

commit 0935ee60 ("selftests: netfilter: add test case for recent mismatch bug")
added a regression check for incorrect initial fill of the result map
that was fixed with 791a615b ("netfilter: nf_set_pipapo: fix initial map fill").

The test used 'nft get element', i.e., control plane checks for
match/nomatch results.

The control plane however doesn't use avx2 version, so we need to
send+match packets.

As the additional packet match/nomatch is slow, don't do this for
every element added/removed: add and use maybe_send_(no)match
helpers and use them.

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