Add default block in DnsOpCode (#11328)

Motivation:

Every switch block should also have a default case.

Modification:

Add default block in DnsOpCode to ensure we not fall-through by mistake

Result:

Cleanup

Signed-off-by: xingrufei <xingrufei@sogou-inc.com>

codec-dns/src/main/java/io/netty/handler/codec/dns/DnsOpCode.java

@@ -65,6 +65,8 @@ public class DnsOpCode implements Comparable<DnsOpCode> {
             return NOTIFY;
         case 0x05:
             return UPDATE;
+        default:
+            break;
         }
 
         return new DnsOpCode(b);