A keyslot not bound to any segment can store any key for any purpose.
To easily check slot status, new enum value is introduced.
This status is valid only for LUKS2, so the functions are backward compatible
with LUKS1.
Move all keyring functions to one place and separate LUKS2 specific
code to generic handling.
Also fix possible mismatch if volume key is in keyring but it is not native
LUKS2 device (libarary cannot process such a device properly).
Remove code for handling multiple digests per single keyslot.
Same would apply to segments with the only exception of segment
in-reencryption. We need that exception so that we will not lose
old key digests too early.
with json-c until 0.12.x json_object_array_length returned signed
integer. json-c 0.13.x and later changed return type to unsigned
size_t.
Consider return values less or equal to zero as empty array, otherwise
array is non-empty.
Originally the key description for VK was derived
from segment id. This could lead to ambiguity when
keyslot key is verified and loaded in kernel keyring
using activation functions with CRYPT_ACTIVATE_KEYRING_KEY
flag raised.
