- Introduce virtio_scsi_init_req and virtio_scsi_free_req
- rename qemu_sgl_init_external to qemu_sgl_concat
- move virtio_scsi_parse_req from virtio_scsi_pop_req to callers
and add header length checks to virtio_scsi_parse_req.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>