zio: rename ZIO_TYPE_IOCTL to ZIO_TYPE_FLUSH

The only possible ioctl is a flush, and any other kind of meta-operation
introduced in the future is likely to have different semantics (much
like trim did). So, lets just call it what it is.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #16064

module/os/linux/zfs/vdev_disk.c

@@ -1400,7 +1400,7 @@ vdev_disk_io_start(zio_t *zio)
 	}
 
 	switch (zio->io_type) {
-	case ZIO_TYPE_IOCTL:
+	case ZIO_TYPE_FLUSH:
 
 		if (!vdev_readable(v)) {
 			/* Drive not there, can't flush */

module/os/linux/zfs/vdev_file.c

@@ -242,7 +242,7 @@ vdev_file_io_start(zio_t *zio)
 	vdev_t *vd = zio->io_vd;
 	vdev_file_t *vf = vd->vdev_tsd;
 
-	if (zio->io_type == ZIO_TYPE_IOCTL) {
+	if (zio->io_type == ZIO_TYPE_FLUSH) {
 		/* XXPOLICY */
 		if (!vdev_readable(vd)) {
 			zio->io_error = SET_ERROR(ENXIO);