## Description 

8084 is mentioned to be the default p2p port in docs:
https://docs.sui.io/guides/operator/validator-tasks#connectivity
And validator / transaction RPC port defaults to 8080 already.
So changing the default p2p port from 8080 to 8084 in `P2pConfig`.
I believe the change is backward compatible but lmk otherwise.

## Test plan 

CI

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## Release notes

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- [ ] Protocol: 
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- [ ] CLI: 
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