Base fee calculation error on pre-london fork

[sieniven]

Summary

• When the chain is on pre-london fork (pre EIP 1559), base fee calculations defaults to return INITIAL_BASE_FEE:https://github.com/0xPolygonHermez/cdk-erigon/blob/479635953bfa8335d36f2d8e589d100193b9748e/params/protocol_params.go#L124
• Seems like cdk-erigon does not handle EIP1559 transactions anyway: https://github.com/0xPolygonHermez/cdk-erigon/blob/479635953bfa8335d36f2d8e589d100193b9748e/zk/txpool/pool.go#L710-L713

Context

• The notifications accumulator pipeline will calculate the current block's base fee with CalcBaseFeeZk. However, the function calls CalcBaseFee, which assumes that the chain is on post London fork
• This is problematic because base fee is never set on blocks pre-london fork. In addition, the accumulator channel propagates the initial base fee to the txpool, thus setting the pendingBaseFee on the pool to be INITIAL_BASE_FEE
• Any txs with gas price below INITIAL_BASE_FEE will never be promoted to the pending pool from the baseFee pool

[sieniven]

774 resolves this issue by adding a forkguard on CalcBaseFeeZk to check for pre/post london fork. cc/ @revitteth