vsock: pass sock_rcvlowat to notify_poll_in as target

Passing 1 as the target to notify_poll_in(), we don't honor
what the user has set via SO_RCVLOWAT, going to set POLLIN
and POLLRDNORM, even if we don't have the amount of bytes
expected by the user.

Let's use sock_rcvlowat() to get the right target to pass to
notify_poll_in();
Signed-off-by: NArseniy Krasnov <AVKrasnov@sberdevices.ru>
Reviewed-by: NStefano Garzarella <sgarzare@redhat.com>
Signed-off-by: NPaolo Abeni <pabeni@redhat.com>

net/vmw_vsock/af_vsock.c

@@ -1066,8 +1066,9 @@ static __poll_t vsock_poll(struct file *file, struct socket *sock,
 		if (transport && transport->stream_is_active(vsk) &&
 		    !(sk->sk_shutdown & RCV_SHUTDOWN)) {
 			bool data_ready_now = false;
+			int target = sock_rcvlowat(sk, 0, INT_MAX);
 			int ret = transport->notify_poll_in(
-					vsk, 1, &data_ready_now);
+					vsk, target, &data_ready_now);
 			if (ret < 0) {
 				mask |= EPOLLERR;
 			} else {