xfs_repair: set NEEDSREPAIR the first time we write to a filesystem

xfs_repair: set NEEDSREPAIR the first time we write to a filesystem

Add a hook to the buffer cache so that xfs_repair can intercept the
first write to a V5 filesystem to set the NEEDSREPAIR flag.  In the
event that xfs_repair dirties the filesystem and goes down, this ensures
that the sysadmin will have to re-start repair before mounting.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>