scsi: do not require a minimum allocation length for REQUEST SENSE

The requirements on the REQUEST SENSE buffer size are not in my copy of SPC
(SPC-4 r27) and not observed by LIO.  Rip them out.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/scsi-bus.c

@@ -427,9 +427,6 @@ static int32_t scsi_target_send_command(SCSIRequest *req, uint8_t *buf)
         }
         break;
     case REQUEST_SENSE:
-        if (req->cmd.xfer < 4) {
-            goto illegal_request;
-        }
         r->len = scsi_device_get_sense(r->req.dev, r->buf,
                                        MIN(req->cmd.xfer, sizeof r->buf),
                                        (req->cmd.buf[1] & 1) == 0);
@@ -538,8 +535,8 @@ SCSIRequest *scsi_req_new(SCSIDevice *d, uint32_t tag, uint32_t lun,
             req = scsi_req_alloc(&reqops_unit_attention, d, tag, lun,
                                  hba_private);
         } else if (lun != d->lun ||
-            buf[0] == REPORT_LUNS ||
-            (buf[0] == REQUEST_SENSE && (d->sense_len || cmd.xfer < 4))) {
+                   buf[0] == REPORT_LUNS ||
+                   (buf[0] == REQUEST_SENSE && d->sense_len)) {
             req = scsi_req_alloc(&reqops_target_command, d, tag, lun,
                                  hba_private);
         } else {