netaddress: Update CNetAddr for ORCHIDv2

Summary:
The original ORCHID prefix was deprecated as of 2014-03, the new
ORCHIDv2 prefix was allocated by RFC7343 as of 2014-07. We did not
consider the original ORCHID prefix routable, and I don't see any reason
to consider the new one to be either.

This is a backport of Core PR15689

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, majcosta, Fabien

Reviewed By: #bitcoin_abc, majcosta, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6210