The default protocol version before initiation is still PV0. Additionally, the QuorumChecker for initiate and reconfig uses PV0 style heartbeats. In order to remove all PV0 code, including PV0 style heartbeat processing, we need the server to only send PV0 style heartbeats when PV0 is enabled. That way if in 3.8 we remove PV0, 3.8 servers will still be able to talk to 3.6 servers running PV1 (but not 3.6 servers running PV0), since they will only send PV1 style heartbeats.