add TODO about createSnapshot

* however, before TODO, keep creating istanbul snapshot

blockchain/blockchain.go

@@ -2151,6 +2151,11 @@ func (bc *BlockChain) insertChain(chain types.Blocks) (int, []interface{}, []*ty
 			}
 		}
 
+		// update governance CurrentSet if it is at an epoch block
+		if bc.engine.CreateSnapshot(bc, block.NumberU64(), block.Hash(), nil) != nil {
+			return i, events, coalescedLogs, err
+		}
+
 		// update governance parameters
 		if istanbul, ok := bc.engine.(consensus.Istanbul); ok {
 			if err = istanbul.UpdateParam(block.NumberU64()); err != nil {

consensus/consensus.go

@@ -127,6 +127,8 @@ type Engine interface {
 	// Protocol returns the protocol for this consensus
 	Protocol() Protocol
 
+	// TODO-kaiax-valset: delete CreateSnapshot which is called after post insert block
+	//  e.g. insertChain, worker.wait, New()
 	// CreateSnapshot does not return a snapshot but creates a new snapshot if not exists at a given point in time.
 	CreateSnapshot(chain ChainReader, number uint64, hash common.Hash, parents []*types.Header) error