consensus: skip all messages during sync (#6577)

Co-authored-by: Aleksandr Bezobchuk

internal/consensus/reactor.go

@@ -1192,11 +1192,6 @@ func (r *Reactor) handleVoteSetBitsMessage(envelope p2p.Envelope, msgI Message)
 // It will handle errors and any possible panics gracefully. A caller can handle
 // any error returned by sending a PeerError on the respective channel.
 //
-// NOTE: We process these messages even when we're fast_syncing. Messages affect
-// either a peer state or the consensus state. Peer state updates can happen in
-// parallel, but processing of proposals, block parts, and votes are ordered by
-// the p2p channel.
-//
 // NOTE: We block on consensus state for proposals, block parts, and votes.
 func (r *Reactor) handleMessage(chID p2p.ChannelID, envelope p2p.Envelope) (err error) {
 	defer func() {
@@ -1206,6 +1201,12 @@ func (r *Reactor) handleMessage(chID p2p.ChannelID, envelope p2p.Envelope) (err
 		}
 	}()
 
+	// Just skip the entire message during syncing so that we can
+	// process fewer messages.
+	if r.WaitSync() {
+		return
+	}
+
 	// We wrap the envelope's message in a Proto wire type so we can convert back
 	// the domain type that individual channel message handlers can work with. We
 	// do this here once to avoid having to do it for each individual message type.