SUNRPC: Convert auth_gss pipe detection to work in namespaces

This seems to have been overlooked when we did the namespace
conversion. If a container is running a legacy version of rpc.gssd
then it will be disrupted if the global 'pipe_version' is set by a
container running the new version of rpc.gssd.

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