Allow setup ring through NCCL_RINGS to facilitate testing

[ROCm/rccl commit: 5b03132ace]

projects/rccl/src/graph/connect.cc

@@ -291,6 +291,7 @@ ncclResult_t ncclTopoPostset(struct ncclComm* comm, int* firstRanks, struct nccl
 
   int nc = nChannels*2;
   if (comm->topo->nodes[NET].count == 0 && comm->topo->type == RCCL_TOPO_CR8G) nc = nChannels*3;
+  if (comm->topo->nodes[NET].count && comm->topo->type == RCCL_TOPO_4P2H_ROME) nc = 4*comm->topo->nodes[NET].count;
   int end = std::min((int)ncclMaxNchannels(), std::max(nc, ncclMinNchannels()));
 
   // Duplication should be complete now