UAPI/ioctl: Improve parameter name of ioctl request definition helpers

UAPI/ioctl: Improve parameter name of ioctl request definition helpers

The third parameter to _IOR et al is a type name, not a size. So the
parameter being named "size" is irritating. Rename it to "argtype"
instead to reduce confusion.

There is a very minor chance that this breaks stuff. It only hurts
however if there is a variable (or macro) in userspace that is called
"argtype" *and* it's used in the parameters of _IOR and friends. IMHO
this is negligible because usually definitions making use of these
macros are provided by kernel headers (i.e. us) or if they are
replicated in userspace code, they are replicated and so supposed to
match the kernel definitions (e.g. to make them usable by programs
without the need to update the kernel headers used to compile the
program).

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>