Use NewOject to invoke constructor of NetworkStats.Entry

AllocObject doesn't invoke the constructor, and when working on
Java code we wouldn't expect that stuff initialized in the
constructor wouldn't actually be initialized on instances
created from JNI.

Test: atest NetworkStackIntegrationTests:android.net.NetworkStatsIntegrationTest
Fix: 322456911
Change-Id: Ibc87ab5ebaf02a7bcaa88307511bd3aaea8698ed

service-t/jni/com_android_server_net_NetworkStatsService.cpp

@@ -45,8 +45,14 @@ static jobject statsValueToEntry(JNIEnv* env, StatsValue* stats) {
         return nullptr;
     }
 
+    // Find the constructor.
+    jmethodID constructorID = env->GetMethodID(gEntryClass, "<init>", "()V");
+    if (constructorID == nullptr) {
+        return nullptr;
+    }
+
     // Create a new instance of the Java class
-    jobject result = env->AllocObject(gEntryClass);
+    jobject result = env->NewObject(gEntryClass, constructorID);
     if (result == nullptr) {
         return nullptr;
     }