nilfs2: check size of array structured data exchanged via ioctls

Although some ioctls of nilfs2 exchange data in the form of indirectly
referenced array, some of them lack size check on the array elements.

This inserts the missing checks and rejects requests if data of ioctl
does not have a valid format.

We usually don't have to check size of structures that we associated
with ioctl commands because the size is tested implicitly for
identifying ioctl command; the checks this patch adds are for the
cases where the implicit check is not applied.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>