fix on number of samples for blocks (#5826)

eth_gasPrice(): A maximum of 3 samples should be taken per block (see
sample const)
The getBlockPrices() function takes 3 samples on the first block and one
on the others.
In the check s.Len() >= limit s.Len() after first block will contain 3
samples and so the loop will be executed only one time for each block
NOT three times

eth/gasprice/gasprice.go

@@ -254,7 +254,8 @@ func (oracle *Oracle) getBlockPrices(ctx context.Context, blockNum uint64, limit
 	txs := newTransactionsByGasPrice(plainTxs, baseFee)
 	heap.Init(&txs)
 
-	for txs.Len() > 0 {
+	count := 0
+	for count < limit && txs.Len() > 0 {
 		tx := heap.Pop(&txs).(types.Transaction)
 		tip := tx.GetEffectiveGasTip(baseFee)
 		if ignoreUnder != nil && tip.Lt(ignoreUnder) {
@@ -263,9 +264,7 @@ func (oracle *Oracle) getBlockPrices(ctx context.Context, blockNum uint64, limit
 		sender, _ := tx.GetSender()
 		if err == nil && sender != block.Coinbase() {
 			heap.Push(s, tip)
-			if s.Len() >= limit {
-				break
-			}
+			count = count + 1
 		}
 	}
 	return nil