Flow telemetry should be cleared when creating a new flow

[DanG100]

We ran into an issue where we have a test that

1. Configures a flow "Flow" and runs traffic
2. Checks counters
3. Configures dut to not forward traffic
4. Configures a flow "Flow" and runs traffic
5. Checks counter

After the 2nd flow, over gNMI the RX counters are from the first flow.

we worked around this by giving each flow a unique name.