Revert "internal/ethapi: don't return header size from rpc (ethereum#…

…27347)"

This reverts commit 49ed215.

internal/ethapi/api.go

@@ -1237,6 +1237,7 @@ func RPCMarshalHeader(head *types.Header) map[string]interface{} {
 		"miner":            head.Coinbase,
 		"difficulty":       (*hexutil.Big)(head.Difficulty),
 		"extraData":        hexutil.Bytes(head.Extra),
+		"size":             hexutil.Uint64(head.Size()),
 		"gasLimit":         hexutil.Uint64(head.GasLimit),
 		"gasUsed":          hexutil.Uint64(head.GasUsed),
 		"timestamp":        hexutil.Uint64(head.Time),