Enable new ancestor/descendants chains limit at fork

Summary:
This enables longer ancestor/descendants chain at phonon fork time.

Depends on D5243

Test Plan:
Update mempool_packages test to test both pre- and postfork limits.
./test_runner && ./test_runner --with-phonon && make check

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, jasonbcox, deadalnix

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, jasonbcox, deadalnix

Subscribers: deadalnix, Fabien, jasonbcox, markblundeberg

Differential Revision: https://reviews.bitcoinabc.org/D5244