netfilter: ctnetlink: fix crash during expectation creation

This patch fixes a possible crash due to the missing initialization
of the expectation class when nf_ct_expect_related() is called.
Reported-by: NBORBELY Zoltan <bozo@andrews.hu>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: NPatrick McHardy <kaber@trash.net>

net/netfilter/nf_conntrack_netlink.c

@@ -1780,6 +1780,7 @@ ctnetlink_create_expect(struct nlattr *cda[], u_int8_t u3, u32 pid, int report)
 		goto out;
 	}
 
+	exp->class = 0;
 	exp->expectfn = NULL;
 	exp->flags = 0;
 	exp->master = ct;