cmd, eth, internal, les: add txfee cap (#21212)

* cmd, eth, internal, les: add gasprice cap

* cmd/utils, eth: add default value for gasprice cap

* all: use txfee cap

* cmd, eth: add fix

* cmd, internal: address comments

les/api_backend.go

@@ -262,6 +262,10 @@ func (b *LesApiBackend) RPCGasCap() *big.Int {
 	return b.eth.config.RPCGasCap
 }
 
+func (b *LesApiBackend) RPCTxFeeCap() float64 {
+	return b.eth.config.RPCTxFeeCap
+}
+
 func (b *LesApiBackend) BloomStatus() (uint64, uint64) {
 	if b.eth.bloomIndexer == nil {
 		return 0, 0