Fix automatic optimizer LR with DDP training (#18641)

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>
Co-authored-by: Ultralytics Assistant <135830346+UltralyticsAssistant@users.noreply.github.com>

ultralytics/engine/trainer.py

@@ -271,6 +271,7 @@ class BaseTrainer:
         )
         if world_size > 1:
             self.model = nn.parallel.DistributedDataParallel(self.model, device_ids=[RANK], find_unused_parameters=True)
+            self.set_model_attributes()  # set again after DDP wrapper
 
         # Check imgsz
         gs = max(int(self.model.stride.max() if hasattr(self.model, "stride") else 32), 32)  # grid size (max stride)