The keyfile interface was designed, well, for keyfiles.

Unfortunately, a keyfile can be placed on a device and the size_t offset
can overflow.

We have to introduce new set of fucntions that allows 64bit offsets even on 32bit systems:
 - crypt_resume_by_keyfile_device_offset
 - crypt_keyslot_add_by_keyfile_device_offset
 - crypt_activate_by_keyfile_device_offset
 - crypt_keyfile_device_read

The new functions have added _device_ in name.

Old functions are just internall wrappers around these.

Also cryptsetup --keyfile-offset and --new-keyfile-offset must now
process 64bit offsets.

For more info see issue 359.