orangefs: set up operation vectors at iget time

Inode, file and address space operations must not change over the lifetime of
an inode.  Make sure we always set them up in iget instead of later during
open/mmap/getattr.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mike Marshall <hubcap@omnibond.com>