Zap data pointer from USBPacket, add a QEMUIOVector instead.
Add a bunch of helper functions to manage USBPacket data.
Switch over users to the new interface.
Note that USBPacket->len was used for two purposes: First to
pass in the buffer size and second to return the number of
transfered bytes or the status code on async transfers. There
is a new result variable for the latter. A new status code
was added to catch uninitialized result.
Nobody creates iovecs with more than one element (yet).
Some users are (temporarely) limited to iovecs with a single
element to keep the patch size as small as possible.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
