discovery/sync_manager: restart historical sync on first connected peer
discovery/sync_manager: restart historical sync on first connected peer

To handle the case where we have been without peers, and get a new
connection, we reset the historical scan booleans when the first active
syncer is connected to trigger another historical sync.

LightningNetwork/lnd,LightningNetwork/lnd,aakselrod/lnd,aakselrod/lnd