NFSv4: Retrieve attributes _before_ calling delegreturn

In order to retrieve cache consistency attributes before
anyone else has a chance to change the inode, we need to
put the GETATTR op _before_ the DELEGRETURN op.

We can then use that as part of a 'nfs_post_op_update_inode_force_wcc()'
call, to ensure that we update the attributes without clearing our
cached data.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>