Add the possibility to swap the layouts between to files.
This feature will be used to migrate files inside Lustre (eg for rebalance) and by HSM to restore files from archive
This patch is the mdd part of the feature, the high level design is:
– Start transaction
– Read LOV EA from obj1 & obj 2
– Run xattr_set(obj1, layout2) & xattr_set(obj2, layout1)
(LOD should not take any action)
– Stop transaction