PPP not raise event NetworkLinkConnectedChanged

NetworkController.NetworkLinkConnectedChanged not invoked with PPP.

The connection is established correctly, event NetworkAddressChanged was invoked, but
event NetworkLinkConnectedChanged was not.

Tested on SCM20260, RC1, GSM: ublox SARA G340 and G350
On NETMF GSM worked correctly.

Someone else please check if you get a NetworkController.NetworkLinkConnectedChanged event via PPP