Create ActiveConnectionMonitor after all objects and observer registrations because, activatableList is filled in constructor of NetworkInterfaceMonitor and
updated in registerObserver methods.

Q: Why is this necessary?

A: In a default installation of a distro, NM creates a "Auto ethx" connection and since this is a system wide connection and ActiveConnectionMonitor is constructed
_after_ registration of nmDBusConnectionProvider, KNM does not know about activationState of Auto Ethx connection. This commit fixes this.