TraceContextInterceptor:reduce unnecessary call to the origin method TraceContext#traceId() (#3313)

apm-sniffer/apm-toolkit-activation/apm-toolkit-trace-activation/src/main/java/org/apache/skywalking/apm/toolkit/activation/trace/TraceContextInterceptor.java

@@ -32,13 +32,13 @@ public class TraceContextInterceptor implements StaticMethodsAroundInterceptor {
 
     @Override public void beforeMethod(Class clazz, Method method, Object[] allArguments, Class<?>[] parameterTypes,
         MethodInterceptResult result) {
-
+        result.defineReturnValue(ContextManager.getGlobalTraceId());
     }
 
     @Override
     public Object afterMethod(Class clazz, Method method, Object[] allArguments, Class<?>[] parameterTypes,
         Object ret) {
-        return ContextManager.getGlobalTraceId();
+        return ret;
     }
 
     @Override