core, eth, les: fix messy code (#15367)

* core, eth, les: fix messy code

* les: fixed tx status test and rlp encoding

* core: add a workaround for light sync

eth/protocol.go

@@ -97,7 +97,7 @@ var errorToString = map[int]string{
 
 type txPool interface {
 	// AddRemotes should add the given transactions to the pool.
-	AddRemotes([]*types.Transaction) error
+	AddRemotes([]*types.Transaction) []error
 
 	// Pending should return pending transactions.
 	// The slice should be modifiable by the caller.