NetDevice up/down consistency and event chain

There is some inconsitency among the working of NetDevices and IP Interfaces. Ideally when a NetDevice changes it state, it should get reflected in IP Interface also. i.e When a NetDevice goes down, associated IP Interface should also go down. When IP Interface goes down, it triggers related events such as DHCP IP address renegotiation, MIP implementation, etc. Currently this is not happening as expected. IP Interfaces, both IPv4 and IPv6 does not respond to state change of NetDevices. This project aims at fixing this behavior, provide the documentation about what is the standard behavior, and what NetDevices are actually implementing it in the right way.