Constant uapi::IOCPARM_MASK

pub const IOCPARM_MASK: u64 = (1 << IOCPARM_SHIFT) - 1; // 8_191u64

[IOCPARAM_SHIFT][https://github.com/DragonFlyBSD/DragonFlyBSD/blob/v5.9.0/sys/sys/ioccom.h]