NFS: Move nfs_probe_destination() into the generic client

And rename it to nfs_probe_server(). I also change it to take the nfs_fh
as an argument so callers can choose what filehandle to probe.

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