Merge changes from topic 'packet-keepalive-fixes' into mnc-dr-dev

* changes:
  Require the new PACKET_KEEPALIVE_OFFLOAD permission.
  Add an error code for generic hardware error.
  Fix bugs and crashes in PacketKeepalive API.
  Add tests for the PacketKeepalive API.
  Add a PACKET_KEEPALIVE_OFFLOAD permission.
  Use a CountDownLatch instead of sleep() in NetworkFactory tests.
  Get rid of shortSleep() in ConnectivityServiceTest.
  Make ConnectivityServiceTest a bit more readable.