Update documentation for ovs-pipeline table number

[qiyueyao]

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Describe the bug After the merge of Flexible pipeline, table numbers are no longer the same with instructions in docs/design/ovs-pipeline.md.

Describe what you are trying to do I am using ovs-ofctl dump-flows for dev testing, following the table numbers in the out-dated documentation no longer provides desired flows.

Describe the support needed Update the table numbers, in case it is flexible, change the instructions for dumping the flows/remove incorrect table numbers/add how to get table numbers.