hw/usb-ohci: Honour endpoint maximum packet size

hw/usb-ohci: Honour endpoint maximum packet size

Honour the maximum packet size for endpoints; this applies when
sending non-isochronous data and means we transfer only as
much as the endpoint allows, leaving the transfer descriptor
on the list for another go next time around. This allows
usb-net to work when connected to an OHCI controller model.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>