LeoHLee

As stated in [the Istanbul BFT paper](https://arxiv.org/pdf/2002.03613.pdf), Istanbul BFT "has O(n^2) communication complexity during both normal case operation and round changes". [The QBFT spec](https://entethalliance.github.io/client-spec/qbft_spec.htm) also states a "message complexity of...

#### System information Geth version: `1.13.14` CL client & version: e.g. [email protected] OS & Version: Linux #### Expected behaviour Sync mainnet state and chaindata after startup. #### Actual behaviour ```...