NFS: Fix SETCLIENTID fallback if GSS is not available

Commit 79d852bf "NFS: Retry SETCLIENTID with AUTH_SYS instead of
AUTH_NONE" did not take into account commit 23631227

 "NFSv4: Fix the
fallback to AUTH_NULL if krb5i is not available".

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>