Only set minNchannels if we are actually using MSCCL, checked using comm->mscclCompatible. (#1337)

src/graph/connect.cc

@@ -691,7 +691,9 @@ ncclResult_t ncclTopoPostset(struct ncclComm* comm, int* firstRanks, int* treePa
   if (mscclEnabled() && (comm->topo->mscclEnabled || mscclForceEnabled())) {
     int mscclNumChannelsRequired = maxNchannels;
     mscclSchedulerInit(comm, &mscclNumChannelsRequired);
-    minNchannels = std::max(minNchannels, mscclNumChannelsRequired);
+    if (comm->mscclCompatible) {
+      minNchannels = std::max(minNchannels, mscclNumChannelsRequired);
+    }
   }
 
   // Honor NCCL_MIN_NRINGS/NCCL_MAX_NRINGS.