The check added here (in #5732/#5733) is supposed to disconnect behind
peers when the current node is syncing, but actually disconnects behind
peers always.
We are syncing when `target > our_height`, but the check here triggers
when `target > remote_height`, which is basically always true when the
preceding `m_core.have_block(hshd.top_id)` check is true.
adc16d2504