core, eth, miner: enforce configured mining reward post 1559 too

[karalabe]

Pre-1559, the transaction pool of a miner only tracked transactions that paid above the configured threshold. Post-1559 however, when the basefee rises, the tip can go below the expected threshold. This PR adds a filtering mechanism when retrieving the txs that can enforce the effective tip.

The PR solved the issue in the txpool because this way "local" tracking and price filtering remains scoped in the pool as previously. The downside is that the filtering needs to check all txs returned every time which is O(n). A more optimal solution would be to return the pending txs as before and check the effective tip in the miner before accepting the next best tx, but that would require leaking the locals and the configured threshold into the miner package.

[rjl493456442]

lgtm