core: check effective tip in txpool pricelimit validation (ethereum#23855)

The price limit is supposed to exclude transactions with too low fee
amount. Before EIP-1559, it was sufficient to check the limit against
the gas price of the transaction. After 1559, it is more complicated
because the concept of 'transaction gas price' does not really exist.

When mining, the price limit is used to exclude transactions below a
certain effective fee amount. This change makes it apply the same check
earlier, in tx validation. Transactions below the specified fee amount
cannot enter the pool.

Fixes ethereum#23837

Author: fjl

core/tx_pool.go

@@ -621,8 +621,9 @@ func (pool *TxPool) validateTx(tx *types.Transaction, local bool) error {
 	if err != nil {
 		return ErrInvalidSender
 	}
-	// Drop non-local transactions under our own minimal accepted gas price or tip
-	if !local && tx.GasTipCapIntCmp(pool.gasPrice) < 0 {
+	// Drop non-local transactions under our own minimal accepted gas price or tip.
+	pendingBaseFee := pool.priced.urgent.baseFee
+	if !local && tx.EffectiveGasTipIntCmp(pool.gasPrice, pendingBaseFee) < 0 {
 		return ErrUnderpriced
 	}
 	// Ensure the transaction adheres to nonce ordering