Fix ioctl numbers on BSDs (#926)

`<sys/ioccom.h>` defines `IOC_OUT` as `0x40000000UL`. But this is "out"
from the perspective of the kernel, not the application. So this
corresponds to `READ` rather than `WRITE`.

Tested on FreeBSD with Smithay/drm-rs#180. This also
seems to be correct for NetBSD and OpenBSD.

src/ioctl/bsd.rs

@@ -18,7 +18,10 @@ pub(super) const fn compose_opcode(
     dir | num | (group << 8) | ((size & IOCPARAM_MASK) << 16)
 }
 
+// `IOC_VOID`
 pub const NONE: RawOpcode = 0x2000_0000;
-pub const WRITE: RawOpcode = 0x4000_0000;
-pub const READ: RawOpcode = 0x8000_0000;
+// `IOC_OUT` ("out" is from the perspective of the kernel)
+pub const READ: RawOpcode = 0x4000_0000;
+// `IOC_IN`
+pub const WRITE: RawOpcode = 0x8000_0000;
 pub const IOCPARAM_MASK: RawOpcode = 0x1FFF;