the server does not obey gnmi path conventions

[gNMI Path Conventions](https://github.com/openconfig/reference/blob/master/rpc/gnmi/gnmi-path-conventions.md) require that the server understands non-keyed list instances, asterisk or ellipsis (`"..."`) as path elements. Non-keyed lists are honored for GET and aggregated SUBSCRIBE operations, the rest is not implemented at all.