Expose CNI args on the DANM API

[Levovar]

Some CNI plugins explicitly depend on arbitrary key-value parameters passed through the "args" field of the CNI spec. For clarification: we are talking about the args field in the network specification field, not the CNI_ARGS parameter set-by the run-time.

By exposing this value on the higher-level network management API CNI plugins can be configured in a more flexible, and dynamic manner. In some cases this might enable the elevation of some CNIs to 100% dynamic status.