ipv6: fix possible mem leaks in ipv6_make_skb()

ip6_setup_cork() might return an error, while memory allocations have
been done and must be rolled back.

Fixes: 6422398c ("ipv6: introduce ipv6_make_skb")
Signed-off-by: NEric Dumazet <edumazet@google.com>
Cc: Vlad Yasevich <vyasevich@gmail.com>
Reported-by: NMike Maloney <maloney@google.com>
Acked-by: NMike Maloney <maloney@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ip6_output.c

@@ -1735,9 +1735,10 @@ struct sk_buff *ip6_make_skb(struct sock *sk,
 	cork.base.opt = NULL;
 	v6_cork.opt = NULL;
 	err = ip6_setup_cork(sk, &cork, &v6_cork, ipc6, rt, fl6);
-	if (err)
+	if (err) {
+		ip6_cork_release(&cork, &v6_cork);
 		return ERR_PTR(err);
-
+	}
 	if (ipc6->dontfrag < 0)
 		ipc6->dontfrag = inet6_sk(sk)->dontfrag;