[BUG] pipeline_paralle is not available when pp_size > 2

[qby10]

This func is wrong, the program will hang because of the "group" variable.

def _batched_p2p_ops( *, tensor_send_prev: Optional[torch.Tensor], tensor_recv_prev: Optional[torch.Tensor], tensor_send_next: Optional[torch.Tensor], tensor_recv_next: Optional[torch.Tensor], group: torch.distributed.ProcessGroup )

after modified:

def _batched_p2p_ops( *, tensor_send_prev: Optional[torch.Tensor], tensor_recv_prev: Optional[torch.Tensor], tensor_send_next: Optional[torch.Tensor], tensor_recv_next: Optional[torch.Tensor] )