PacketBuilder: add IPv6 fragment packets support am: d83596f567 am: 67a6c7939b

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2988170

Change-Id: Iffac20e94e281ac072128f996515f2632fb33aaa
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>