Move Tether4Key and Tether4Value to common libs

EthernetTetheringTest needs to parse BPF map content for IPv4
forwarding rule tests. Move the struct class files to common
libs.

Compare Tether4{Key, Value}.java between frameworks/libs/net/common
and packages/modules/Connectivity/Tethering.
There is only the package name change as expected.

$ diff packages/modules/Connectivity/Tethering/src/com/android/networkstack/tethering/Tether4Key.java frameworks/libs/net/common/device/com/android/net/module/util/bpf/Tether4Key.java
17c17
< package com.android.networkstack.tethering;
---
> package com.android.net.module.util.bpf;

$ diff packages/modules/Connectivity/Tethering/src/com/android/networkstack/tethering/Tether4Value.java frameworks/libs/net/common/device/com/android/net/module/util/bpf/Tether4Value.java
17c17
< package com.android.networkstack.tethering;
---
> package com.android.net.module.util.bpf;

Test: atest TetheringCoverageTests

Change-Id: I73c180fa4129aefde1e64ecbafe928f388b061d6
8 files changed