netfilter: xt_nat: fix DNAT target for shifted portmap ranges

The commit 2eb0f624 ("netfilter: add NAT support for shifted
portmap ranges") did not set the checkentry/destroy callbacks for
the newly added DNAT target. As a result, rulesets using only
such nat targets are not effective, as the relevant conntrack hooks
are not enabled.
The above affect also nft_compat rulesets.
Fix the issue adding the missing initializers.

Fixes: 2eb0f624 ("netfilter: add NAT support for shifted portmap ranges")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/xt_nat.c

@@ -216,6 +216,8 @@ static struct xt_target xt_nat_target_reg[] __read_mostly = {
 	{
 		.name		= "DNAT",
 		.revision	= 2,
+		.checkentry	= xt_nat_checkentry,
+		.destroy	= xt_nat_destroy,
 		.target		= xt_dnat_target_v2,
 		.targetsize	= sizeof(struct nf_nat_range2),
 		.table		= "nat",