Enable Docstats with totalSizeInBytes for 6.1.0

Relates elastic#27117

Author: dnhatn

core/src/main/java/org/elasticsearch/index/shard/DocsStats.java

@@ -82,7 +82,7 @@ public long getAverageSizeInBytes() {
     public void readFrom(StreamInput in) throws IOException {
         count = in.readVLong();
         deleted = in.readVLong();
-        if (in.getVersion().onOrAfter(Version.V_7_0_0_alpha1)) {
+        if (in.getVersion().onOrAfter(Version.V_6_1_0)) {
             totalSizeInBytes = in.readVLong();
         } else {
             totalSizeInBytes = -1;
@@ -93,7 +93,7 @@ public void readFrom(StreamInput in) throws IOException {
     public void writeTo(StreamOutput out) throws IOException {
         out.writeVLong(count);
         out.writeVLong(deleted);
-        if (out.getVersion().onOrAfter(Version.V_7_0_0_alpha1)) {
+        if (out.getVersion().onOrAfter(Version.V_6_1_0)) {
             out.writeVLong(totalSizeInBytes);
         }
     }