[nfsv4] Directory delegation modification

["Anatoly Pinchuk" <apinchuk at bluearc.com>]

It seems that the protocol does not specify if an already established
directory delegation may be modified. So, it would be beneficial if we
agree on how the server SHOULD/MUST process an attempted modification.
Two possible approaches are:
- Disallow the modification and return an error code if the client tries
to modify the delegation
- Allow the modification and replace all existing delegation fields with
new ones constructed using GET_DIR_DELEGATION arguments
Has anyone considered this issue?

Regards,
Anatoly