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

If the rpcsec_gss_krb5 module cannot be loaded, the attempt to create
an rpc_client in nfs4_init_client will currently fail with an EINVAL.
Fix is to retry with AUTH_NULL.

Regression introduced by the commit "NFS: Use "krb5i" to establish NFSv4
state whenever possible"
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Bryan Schumaker <bjschuma@netapp.com>

fs/nfs/nfs4client.c

@@ -200,6 +200,8 @@ struct nfs_client *nfs4_init_client(struct nfs_client *clp,
 
 	__set_bit(NFS_CS_DISCRTRY, &clp->cl_flags);
 	error = nfs_create_rpc_client(clp, timeparms, RPC_AUTH_GSS_KRB5I);
+	if (error == -EINVAL)
+		error = nfs_create_rpc_client(clp, timeparms, RPC_AUTH_NULL);
 	if (error < 0)
 		goto error;