Extend YNL to support explicit model for rtnetlink message ids

[maryamtahhan]

rtnetlink doesn't seem to fit into unified or directional message enumeration models. It seems like an 'explicit' model would be useful, to require the schema author to specify the message ids directly.

The goal of this task is to extend YNL to support this explicit model and support commands and notifications simultaneously from the same netlink-raw spec.

DOD: Patches submitted to the Kernel