Fix gossipsub handling to process only when in follow state

[austinabell]

Summary of changes
Changes introduced in this pull request:

• Issue is now the bitswap interactions are a bit broken when requesting messages, and it's stalling the chain_sync polling thread
  • This PR does not solve the underlying issue, we will still run into this when we get into follow state, but this check needs to be in place anyway (shouldn't handle gossip events outside of follow state) and I added a TODO and will create an issue for solving the greater issue

Reference issue to close (if applicable)

Closes

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