NFSv4: Ensure continued open and lockowner name uniqueness

In order to enable migration support, we will want to move some of the
structures that are subject to migration into the struct nfs_server.
In particular, if we are to move the state_owner and state_owner_id to
being a per-filesystem structure, then we should label the resulting
open/lock owners with a per-filesytem label to ensure global uniqueness.

This patch does so by adding the super block s_dev to the open/lock owner
name.

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