feat(p2p): channels with limit of send and recv rate

[lklimek]

Issue being fixed or feature implemented

Mempool sync can DoS a node by sending thousands of transactions and filling whole p2p connection.

What was done?

Introduced new type of channel that can limit send and receive rate of messages and implemented it for mempool.

Changed ChannelIterator to interface, to allow multiple implementations, and implemented throttledChannelIterator to read from channel with recv rate limits applied.

Introduced new [mempool] settings (disabled by default):

• tx-send-rate-limit is the rate limit for sending transactions to peers, in transactions per second.
• tx-recv-rate-limit is the rate limit for receiving transactions from peers, in transactions per second.
• tx-recv-rate-punish-peer set to true means that when tx-recv-rate-limit is reached, the peer will be punished (disconnected).

How Has This Been Tested?

Added unit tests

Tested during Dash Platform load testing.

Breaking Changes

None

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

[shumkov]

👍