P2P DoS prevention

[leoluk]

Anyone can talk on the p2p gossip channel and send invalid lockup observations.

• Figure out what protections libp2p provides.
• Channel pressure in guardiand at high rates.
• Inbound VAAs should only create a vaaState entries if they're valid.
• How expensive is the validation?
• Whitelist libp2p peers? We already verify those signatures anyway.

https://github.com/certusone/wormhole/blob/c370a94911c3b06237fd5e92837739ff2f98d191/bridge/cmd/guardiand/processor.go#L221

[leoluk]

Dropping from launch blockers since we cannot adjust fees dynamically due to Solana VM limitations.

Bridge-side DoS prevention can be fixed in a follow-up.

[leoluk]

https://github.com/libp2p/specs/blob/master/pubsub/gossipsub/gossipsub-v1.1.md