Decouple Netvirt L2 and L3

Considering the various cni plugins available already, It is desirable to have a pure l3 model for COE as well.

The current POC implementation uses L2 to communicate between all pods within the same node, and uses L3 only across nodes. This was done because the current netvirt model has a tight coupling between L2 and L3. This needs to be refactored