Move NattKeepalivePacketData out of the framework

For implementing parcelable interface for NattKeepalivePacketData.
Move this class out of framework.jar and move to services.jar

This class is used in telephony-common.jar and it also loads
service.jar.

Bug: 33530442
Test: - build pass
      - atest NetworkStackTests
      - atest ConnectivityServiceTest

Change-Id: Id2fdec5c4015d2cefd8a93e0cfdcc3c304fc9b64