message: Fix the packing
  Summary:
  V2 is slightly different
  Ref T15355
  Test Plan: pipelining passes
  Reviewers: #tensorflow, #framework_ip_review_-_any_oss_or_third-party_code_use_has_been_approved, hakons
  Maniphest Tasks: T15355
diff: @@ -21,6 +21,7 @@ from tensorflow.compiler.plugin.poplar.ops import gen_functional_ops
  from tensorflow.python.framework import func_graph as func_graph_module
  from tensorflow.python.framework import ops
  from tensorflow.python.ipu import functional_ops_grad
  +from tensorflow.python.ops import cond_v2
  from tensorflow.python.ops import control_flow_util_v2 as util
  @@ -38,8 +39,7 @@ def _pipeline_stage_grad(op, *grads):
  Tout=func_grad_graph.output_types,
  output_shapes=func_grad_graph.output_shapes,
  stage_id=stage_id)
  - return func_graph_module.pack_sequence_as(func_grad_graph.structured_outputs,
  - outputs)
  + return cond_v2._pack_sequence_as(func_grad_graph.structured_outputs, outputs) # pylint: disable=protected-access
  @ops.RegisterGradient("Pipeline")
  