Merge pull request ethereum#1384 from maticnetwork/manav/fix-invalid-validator-set

Use `header.ParentHash` while fetching validator set from child chain contract so that while making the call, it uses the state which belongs to the same fork which is being imported.

Author: manav2401

consensus/bor/bor.go

@@ -468,8 +468,9 @@ func (c *Bor) verifyCascadingFields(chain consensus.ChainHeaderReader, header *t
 
 	// Verify the validator list match the local contract
 	if IsSprintStart(number+1, c.config.CalculateSprint(number)) {
-		newValidators, err := c.spanner.GetCurrentValidatorsByBlockNrOrHash(context.Background(), rpc.BlockNumberOrHashWithNumber(rpc.LatestBlockNumber), number+1)
-
+		// Use parent block's hash to make the eth_call to fetch validators so that the state being
+		// used to make the call is of the same fork.
+		newValidators, err := c.spanner.GetCurrentValidatorsByBlockNrOrHash(context.Background(), rpc.BlockNumberOrHashWithHash(header.ParentHash, false), number+1)
 		if err != nil {
 			return err
 		}