dm_ioctl

Rename crate to dm_ioctl; change version to 4.48.0; expose version constant.

Remove the unused DM_DIR and DM_CONTROL_NODE constants.

Actually use DM_MAX_TYPE_NAME. Document size-limit constants.

Move DM_NAME_LIST_* to a new public bitflags type, DmNameListFlags.

Remove unused FlexibleArrayMember functionality.