xfs/ima: Regression caching i_version

[Frederick Lawler <fred@cloudflare.com>]

Hi Jeff,

While testing 6.18, I think I found a regression with
commit 1cf7e834a6fb ("xfs: switch to multigrain timestamps") since 6.13
where IMA is no longer able to properly cache i_version when we overlay
tmpfs on top of XFS. Each measurement diff check in function
process_measurement() reports that the i_version is
always set to zero for iint->real_inode.version.

The function ima_collect_measurement() is looking to extract the version
from the cookie on next measurement to cache i_version.

I'm unclear from the commit description what the right approach here is:
update in IMA land by checking for time changes, or do
something else such as adding the cookie back.

Thanks,
Fred