Add TcpKeepalivePacketData to SystemApi am: 103ec4aa8d am: a232c68028 am: 40190840bb

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1494038

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I1aa9deefefcaf75959463e8a8a87bfeefb98f0ee