Revert "Stop always storing blocks from whitelisted peers"

Summary:
This reverts commit c3f4936b0453a0d60d1a41a2ee6557f8fb2d9f86.

D2246 appears to have a dependency on 015a5258adffb0cf394f387a95ac9c8afc34cfc3
which was not included and breaks p2p-fullblocktest

Test Plan: test_runner.py p2p-fullblocktest

Reviewers: deadalnix, Fabien, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2252