Secondary cannot restart replication

After SERVER-33747, initial_sync_document_validation.js times out on 3.6. The problem is that my SERVER-33747 change, ReplicationCoordinatorImpl::_startDataReplication exits early if it's ever been called before. The sequence _startDataReplication -> _stopDataReplication -> _startDataReplication therefore no longer actually restarts data replication.

This shows up in initial_sync_document_validation.js because this test calls the "resync" command. The "resync" command was removed after 3.6 (SERVER-31239) leaving ReplicationCoordinatorImpl::resyncData with one caller, replSetSyncFrom, the method was completely removed after 4.4 (SERVER-46831).

Does the replSetSyncFrom command suffer the same deadlock? In all versions?