Re-enable etcd endpoint auto-sync

Removing this in 002e6c4 regressed
control-plane-only nodes, as we rely on the etcd client to update its
endpoint list internally so that we can use it to sync the load-balancer
address list.

Signed-off-by: Brad Davidson <brad.davidson@rancher.com>

pkg/etcd/etcd.go

@@ -681,6 +681,7 @@ func getClientConfig(ctx context.Context, control *config.Control, endpoints ...
 		DialTimeout:          defaultDialTimeout,
 		DialKeepAliveTime:    defaultKeepAliveTime,
 		DialKeepAliveTimeout: defaultKeepAliveTimeout,
+		AutoSyncInterval:     defaultKeepAliveTimeout,
 		PermitWithoutStream:  true,
 	}