On udp sockets, ioctl SIOCINQ returns the payload size of the first
packet. Since commit e6afc8ac pulled the headers, the result is
incorrect when subtracting header length. Remove that operation.

Fixes: e6afc8ac ("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>