nfscl: Disable use of the LookupOpen RPC

The LookupOpen RPC reduces the number of Open RPCs
needed. Unfortunately, it breaks certain software
builds over NFS, so disable it until this is fixed.

The LookupOpen RPC is only used for NFSv4.1/4.2
mounts when the "oneopenown" mount option is
specified, so this should not affect many users.