xfs: miscellaneous repair tweaks [v26.1]

Before we start adding online repair functionality, there's a few tweaks
that I'd like to make to the common repair code.  First is a fix to the
integration between repair and the health status code that was
interfering with repair re-evaluations.  Second is a minor tweak to the
sole existing repair functions to make one last check that the user
hasn't terminated the calling process before we start writing to the
filesystem.  This is a pattern that will repeat throughout the rest of
the repair functions.

This has been running on the djcloud for years with no problems.  Enjoy!

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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