[IT03] Add replacement methods for network activity

Reference for NMS in ConnectivityManager should be removed for
incoming CS mainline. The API for listening network activity
should not go into NMS. As an alternative, the registry requests
should be sent to CS and handled by CS. Add necessary alternative
in IConnectivityManger first. The detail implementation will be
added in the follow up commits.

Bug: 170598012
Test: m
Change-Id: If4d24b937feb88a61f22073af2f671cf20298364