Reenable MNNVL backend for FlashInfer allreduce fusion

python/sglang/srt/layers/communicator.py

@@ -163,7 +163,7 @@ def apply_flashinfer_allreduce_fusion(batch_size: int):
         and batch_size > 0
         and batch_size <= FUSE_ALLREDUCE_MAX_BATCH_SIZE
         and not is_dp_attention_enabled()
-        and get_global_server_args().enable_flashinfer_allreduce_fusion
+        and get_global_server_args().flashinfer_allreduce_fusion_backend is not None
         and not is_flashinfer_allreduce_unavailable()
     )