usb-redir: Add an already_in_flight packet-id queue

After a live migration, the usb-hcd will re-queue all packets by
walking over the schedule in the guest memory again, but requests which
were encountered on the migration source before will already be in flight,
so these should *not* be re-send to the usbredir-host.

This patch adds an already in flight packet ud queue, which will be filled by
the source before migration and then moved over to the migration dest, any
async handled packets are then checked against this queue to avoid sending
the same packet to the usbredir-host twice.

Signed-off-by: Hans de Goede <hdegoede@redhat,com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
