NFS: Request a directory delegation during RENAME

NFS: Request a directory delegation during RENAME

If we notice that we're renaming a file within a directory then we take
that as a sign that the user is working with the current directory and
may want a delegation to avoid extra revalidations when possible.

The nfs_request_directory_delegation() function exists within the NFS v4
module, so I add an extra flag to rename_setup() to indicate if a dentry
is being renamed within the same parent directory.

Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>