netfilter: expect: fix crash when putting uninited expectation

We crash in __nf_ct_expect_check, it calls nf_ct_remove_expect on the
uninitialised expectation instead of existing one, so del_timer chokes
on random memory address.

Fixes: ec0e3f01114ad32711243 ("netfilter: nf_ct_expect: Add nf_ct_remove_expect()")
Reported-by: Sergey Kvachonok <ravenexp@gmail.com>
Tested-by: Sergey Kvachonok <ravenexp@gmail.com>
Cc: Gao Feng <fgao@ikuai8.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_expect.c

@@ -422,7 +422,7 @@ static inline int __nf_ct_expect_check(struct nf_conntrack_expect *expect)
 	h = nf_ct_expect_dst_hash(net, &expect->tuple);
 	hlist_for_each_entry_safe(i, next, &nf_ct_expect_hash[h], hnode) {
 		if (expect_matches(i, expect)) {
-			if (nf_ct_remove_expect(expect))
+			if (nf_ct_remove_expect(i))
 				break;
 		} else if (expect_clash(i, expect)) {
 			ret = -EBUSY;