Test INVERT matching for prefix-sets

[wenovus]

No description provided.

[DanG100]

LGTM, though same concern around complexity of the attributes test

[wenovus]

 policy_test.go:164: Replace(t) on ygnmi client (target: \"dut2\") at /network-instances/network-instance[name=DEFAULT]/protocols/protocol[identifier=BGP][name=BGP]/bgp/neighbors/neighbor[neighbor-address=127.0.0.2]/apply-policy/config/default-import-policy: Replace(t) at path origin:\"openconfig\"  elem:{name:\"network-instances\"}  elem:{name:\"network-instance\"  key:{key:\"name\"  value:\"DEFAULT\"}}  elem:{name:\"protocols\"}  elem:{name:\"protocol\"  key:{key:\"identifier\"  value:\"BGP\"}  key:{key:\"name\"  value:\"BGP\"}}  elem:{name:\"bgp\"}  elem:{name:\"neighbors\"}  elem:{name:\"neighbor\"  key:{key:\"neighbor-address\"  value:\"127.0.0.2\"}}  elem:{name:\"apply-policy\"}  elem:{name:\"config\"}  elem:{name:\"default-import-policy\"}: rpc error: code = Internal desc = update is stale, update is stale, update is stale: notification:",