Move Struct.java to com.android.net.module.util package. am: 19c4a3c47e am: 9f1d69a016

Original change: https://android-review.googlesource.com/c/platform/frameworks/libs/net/+/1532061

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Iee71b8fe404104277b0970f6e6e72703af94caf6