remove the di_uid/di_gid fields from the XFS icdinode

[Christoph Hellwig <hch@xxxxxx>]

Hi all,

this series removes the duplicate di_uid/di_gid fields in the XFS
icdinode and alwasys uses the VFS inode fields.  It also matches the
user namespace used by other file systems instead of always using
init_user_ns.  For now that change is mostly theoretical, but it might
be more useful with some of the pending VFS changes in that area.