The xHCI controller will ignore the endpoint MTU and so may deliver
packets of any length.  Detect short packets as being any packet that
has a length of zero or a length that is not a multiple of the MTU.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
Message-Id: <20220906183053.3625472-4-mcb30@ipxe.org>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>