Deprecating the ORIGIN attribute

The BGP Origin attribute in its original meaning has been out of use for years. Yet, the BGP Origin attribute has high priority in the best route selection algorithm, right after the AS Path length, and it's being used inconsistently over the Internet to manipulate the route preference. This document updates RFC 4271 and RFC 7606 by making the BGP Origin attribute half-optional and explicitly allowing its scrubbing to zero (IGP).