netfilter: ctnetlink: use helper function to calculate expect ID

Delete expectation path is missing a call to the nf_expect_get_id()
helper function to calculate the expectation ID, otherwise LSB of the
expectation object address is leaked to userspace.

Fixes: 3c791076 ("netfilter: ctnetlink: don't use conntrack/expect object addresses as id")
Reported-by: zdi-disclosures@trendmicro.com
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_netlink.c

@@ -3420,7 +3420,8 @@ static int ctnetlink_del_expect(struct sk_buff *skb,
 
 		if (cda[CTA_EXPECT_ID]) {
 			__be32 id = nla_get_be32(cda[CTA_EXPECT_ID]);
-			if (ntohl(id) != (u32)(unsigned long)exp) {
+
+			if (id != nf_expect_get_id(exp)) {
 				nf_ct_expect_put(exp);
 				return -ENOENT;
 			}