fix CNode construction in denialofservice_tests.cpp

Summary:
When I landed D10973, I landed the wrong branch with an earlier version of a commit, before applying a fix.
This is the required fixed to unbreak the master branch.

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10983