peer: fix bug in handshake wherein RevokeAndAck would be sent first

This commit fixes a bug in the opening handshake between to peers. The
bug would arise when on or many channels were active between a node
establishing a new connection. The htlcManager goroutines will
immediately attempt to extend the revocation window once they’re
active. However, at this time, the init message may not yet have been
sent as the two executions are in distinct goroutines.

We fix this bug by manually writing the init message directly to the
socket, rather than traveling through the queueHandler goroutine. With
this, we ensure that the init message is _always_ sent first.

peer.go

@@ -287,18 +287,15 @@ func (p *peer) Start() error {
 
 	peerLog.Tracef("peer %v starting", p)
 
-	p.wg.Add(2)
+	// Exchange local and global features, the init message should be very
-	go p.queueHandler()
+	// first between two nodes.
-	go p.writeHandler()
-
-	// Exchange local and global features, the init message should be
-	// very first between two nodes.
 	if err := p.sendInitMsg(); err != nil {
 		return err
 	}
 
-	// Should wait for peers to compare their feature vectors
+	// Before we launch any of the helper goroutines off the peer struct,
-	// and only then start message exchanges.
+	// we'll first ensure proper adherance to the p2p protocl. The init
+	// message MUST be sent before any other message.
 	msg, _, err := p.readNextMessage()
 	if err != nil {
 		return err
@@ -313,7 +310,9 @@ func (p *peer) Start() error {
 			"must be init message")
 	}
 
-	p.wg.Add(3)
+	p.wg.Add(5)
+	go p.queueHandler()
+	go p.writeHandler()
 	go p.readHandler()
 	go p.channelManager()
 	go p.pingHandler()
@@ -1236,16 +1235,15 @@ func (p *peer) handleInitMsg(msg *lnwire.Init) error {
 	return nil
 }
 
-// sendInitMsg sends init message to remote peer which represent our
+// sendInitMsg sends init message to remote peer which contains our currently
-// features local and global vectors.
+// supported local and global features.
 func (p *peer) sendInitMsg() error {
 	msg := lnwire.NewInitMessage(
 		p.server.globalFeatures,
 		p.server.localFeatures,
 	)
 
-	p.queueMsg(msg, nil)
+	return p.writeMessage(msg)
-	return nil
 }
 
 // handleDownStreamPkt processes an HTLC packet sent from the downstream HTLC