By changing encryption sector size during reencryption we may
increase effective logical block size for dm-crypt active device.
For example if hosted filesystem on encrypted data device
has block size set to 512 bytes and we increase dm-crypt logical
size durign reencryption to 4096 bytes it breaks the filesystem.
Do not allow encryption sector size to be increased over value
provided by fs superblock in BLOCK_SIZE property.
The check is applied while initialising LUKS2 device encryption
(reencrypt --encrypt/--new) or when initialising LUKS2 reencryption
on active dm-crypt device.
Note that this check cannot be applied on offline device (data device
is encrypted).
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