minor changes for consistency

Author: SylvainJuge

instrumentation/servlet/servlet-3.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/Servlet3Advice.java

@@ -31,12 +31,11 @@
 @SuppressWarnings("unused")
 public class Servlet3Advice {
 
-  // TODO
   public static class AdviceScope {
-    public CallDepth callDepth;
-    public ServletRequestContext<HttpServletRequest> requestContext;
-    public Context context;
-    public Scope scope;
+    private final CallDepth callDepth;
+    private final ServletRequestContext<HttpServletRequest> requestContext;
+    private final Context context;
+    private final Scope scope;
 
     public AdviceScope(
         CallDepth callDepth,
@@ -61,9 +60,11 @@ && helper().needsRescoping(currentContext, attachedContext)) {
         // Given request already has a context associated with it.
         // see the needsRescoping() javadoc for more explanation
         contextToUpdate = attachedContext;
+        context = null;
       } else {
         // We are inside nested servlet/filter/app-server span, don't create new span
         contextToUpdate = currentContext;
+        context = null;
       }
 
       // Update context with info from current request to ensure that server span gets the best