Use chan struct{} for tx/blockProcessed chans.

These channels are being used as semaphores, so it's more efficient to use
a 0-byte type and allow compiler optimizations for the specific use case.

blockmanager.go

@@ -1018,11 +1018,11 @@ out:
 
 			case *txMsg:
 				b.handleTxMsg(msg)
-				msg.peer.txProcessed <- true
+				msg.peer.txProcessed <- struct{}{}
 
 			case *blockMsg:
 				b.handleBlockMsg(msg)
-				msg.peer.blockProcessed <- true
+				msg.peer.blockProcessed <- struct{}{}
 
 			case *invMsg:
 				b.handleInvMsg(msg)
@@ -1189,7 +1189,7 @@ func (b *blockManager) NewPeer(p *peer) {
 func (b *blockManager) QueueTx(tx *btcutil.Tx, p *peer) {
 	// Don't accept more transactions if we're shutting down.
 	if atomic.LoadInt32(&b.shutdown) != 0 {
-		p.txProcessed <- false
+		p.txProcessed <- struct{}{}
 		return
 	}
 
@@ -1200,7 +1200,7 @@ func (b *blockManager) QueueTx(tx *btcutil.Tx, p *peer) {
 func (b *blockManager) QueueBlock(block *btcutil.Block, p *peer) {
 	// Don't accept more blocks if we're shutting down.
 	if atomic.LoadInt32(&b.shutdown) != 0 {
-		p.blockProcessed <- false
+		p.blockProcessed <- struct{}{}
 		return
 	}
 

peer.go

@@ -168,8 +168,8 @@ type peer struct {
 	sendDoneQueue      chan struct{}
 	queueWg            sync.WaitGroup // TODO(oga) wg -> single use channel?
 	outputInvChan      chan *btcwire.InvVect
-	txProcessed        chan bool
-	blockProcessed     chan bool
+	txProcessed        chan struct{}
+	blockProcessed     chan struct{}
 	quit               chan struct{}
 	StatsMtx           sync.Mutex // protects all statistics below here.
 	versionKnown       bool
@@ -1795,8 +1795,8 @@ func newPeerBase(s *server, inbound bool) *peer {
 		sendQueue:       make(chan outMsg, 1),   // nonblocking sync
 		sendDoneQueue:   make(chan struct{}, 1), // nonblocking sync
 		outputInvChan:   make(chan *btcwire.InvVect, outputBufferSize),
-		txProcessed:     make(chan bool, 1),
-		blockProcessed:  make(chan bool, 1),
+		txProcessed:     make(chan struct{}, 1),
+		blockProcessed:  make(chan struct{}, 1),
 		quit:            make(chan struct{}),
 	}
 	return &p