Linux system call wrappers: truncate ioctl request number to 32 bits

As explained in https://bugs.kde.org/show_bug.cgi?id=331829, when passing
an ioctl request number as an int to a function the request number will
be sign-extended to 64 bits on 64-bit systems. Avoid that this causes
Valgrind to fail to recognize an ioctl by truncating the request number
to 32 bits.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14232 a5019735-40e9-0310-863c-91ae7b9d1cf9