mvcc: keep 64-bit alignment in "store" struct

Signed-off-by: Gyuho Lee <leegyuho@amazon.com>

mvcc/kvstore.go

@@ -77,12 +77,12 @@ type store struct {
 	ReadView
 	WriteView
 
-	cfg StoreConfig
-
 	// consistentIndex caches the "consistent_index" key's value. Accessed
 	// through atomics so must be 64-bit aligned.
 	consistentIndex uint64
 
+	cfg StoreConfig
+
 	// mu read locks for txns and write locks for non-txn store changes.
 	mu sync.RWMutex