nfsd: mark cb path down on unknown errors

An unexpected error is probably a sign that something is wrong with the
callback path.
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4callback.c

@@ -1126,6 +1126,7 @@ static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback
 		}
 		break;
 	default:
+		nfsd4_mark_cb_fault(cb->cb_clp, cb->cb_seq_status);
 		dprintk("%s: unprocessed error %d\n", __func__,
 			cb->cb_seq_status);
 	}