udp: do not expect udp headers on ioctl SIOCINQ

On udp sockets, ioctl SIOCINQ returns the payload size of the first
packet. Since commit e6afc8ace6 pulled the headers, the result is
incorrect when subtracting header length. Remove that operation.

Fixes: e6afc8ace6 ("udp: remove headers from UDP packets before queueing")

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

net/ipv4/udp.c

@@ -1282,8 +1282,6 @@ int udp_ioctl(struct sock *sk, int cmd, unsigned long arg)
 			 * of this packet since that is all
 			 * that will be read.
 			 */
-			amount -= sizeof(struct udphdr);
-
 		return put_user(amount, (int __user *)arg);
 	}