H20's internode RDMA & NVL bandwidth drops to 50% after pr 245

### Environment

- Hardware: 2 nodes × 8× H20 GPUs,
- Network: RoCE, CX6 InfiniBand NICs

### Problem

Internode RDMA bandwidth dropped by ~50% after commit `bc118b` ( pr #245 ) , confirmed via bisect.

the commit before `bc118b` (`9eb2f`)
```shell
[tuning] Best dispatch (FP8): SMs 24, NVL chunk 24, RDMA chunk 4: 44.00 GB/s (RDMA), 144.10 GB/s (NVL)
[tuning] Best dispatch (BF16): SMs 24, NVL chunk 4, RDMA chunk 8: 45.35 GB/s (RDMA), 148.50 GB/s (NVL)
[tuning] Best combine: SMs 24, NVL chunk 1, RDMA chunk 8: 43.93 GB/s (RDMA), 143.85 GB/s (NVL)
```
after commit `bc118b`
```shell
[tuning] Best dispatch (FP8): SMs 24, NVL chunk 8, RDMA chunk 12: 23.18 GB/s (RDMA), 75.91 GB/s (NVL)
[tuning] Best dispatch (BF16): SMs 24, NVL chunk 4, RDMA chunk 12: 23.72 GB/s (RDMA), 77.68 GB/s (NVL)
[tuning] Best combine: SMs 24, NVL chunk 1, RDMA chunk 8: 23.41 GB/s (RDMA), 76.65 GB/s (NVL)
```

I have reviewed the modifications in the submission, but I find them too challenging to grasp. Could the developers reproduce and resolve this issue?