LUKS2 specification allows various size of LUKS2 metadata.
The single metadata instance is composed of LUKS2 binary header
(4096 bytes) and immediately following json area. The resulting
assembled metadata size have to be one of following values,
all in KiB:
16, 32, 64, 128, 256, 512, 1024, 2048 or 4096
auto-recovery triggers any time when only single correct LUKS2
header instance was found. That may be dangerous.
We should suppress auto-recovery in case blkid decided the
device is no longer LUKS device. For example if secondary (intact)
LUKS2 header was left behind and blkid declares the device is LVM2
member.
Moreover if at least one header instance is corrupted and blkid
declares device non-empty and non-LUKS in the same time, header load
operation will be aborted with error.
The code scan for the second header only if primary is corrrupted.
Let's set the possible offsets more clear.
This patch also removes 8kB header offset (that was not supported anyway).
