ipv4: warn once on passing AF_INET6 socket to ip_recv_error

One line change, in response to catching an occurrence of this bug.
See also fix f4713a3dfad0 ("net-timestamp: make tcp_recvmsg call ...")

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_sockglue.c

@@ -414,6 +414,8 @@ int ip_recv_error(struct sock *sk, struct msghdr *msg, int len, int *addr_len)
 	int err;
 	int copied;
 
+	WARN_ON_ONCE(sk->sk_family == AF_INET6);
+
 	err = -EAGAIN;
 	skb = sock_dequeue_err_skb(sk);
 	if (skb == NULL)