server: Broadcast now takes a set of peers to skip

In this commit, we modify the Broadcast to take a *set* of peers to
skip, rather than just a single peer. We make this modification as when
a new channel is discovered, it’s likely the case that we get the
announcement from several peers rather than a single peer. With this
change, we’ll ensure that the caller (who is aware of the set of
senders) is able to properly avoid wasting bandwidth by re-sending the
message to all peers that sent it to us originally.

server.go

@@ -845,7 +845,7 @@ func (s *server) establishPersistentConnections() error {
 // messages to all peers other than the one specified by the `skip` parameter.
 //
 // NOTE: This function is safe for concurrent access.
-func (s *server) BroadcastMessage(skip *btcec.PublicKey,
+func (s *server) BroadcastMessage(skip map[routing.Vertex]struct{},
 	msgs ...lnwire.Message) error {
 
 	s.mu.Lock()
@@ -859,7 +859,7 @@ func (s *server) BroadcastMessage(skip *btcec.PublicKey,
 //
 // NOTE: This method MUST be called while the server's mutex is locked.
 func (s *server) broadcastMessages(
-	skip *btcec.PublicKey,
+	skips map[routing.Vertex]struct{},
 	msgs []lnwire.Message) error {
 
 	srvrLog.Debugf("Broadcasting %v messages", len(msgs))
@@ -869,10 +869,13 @@ func (s *server) broadcastMessages(
 	// throughout this process to ensure we deliver messages to exact set
 	// of peers present at the time of invocation.
 	var wg sync.WaitGroup
-	for pubStr, sPeer := range s.peersByPub {
-		if skip != nil && sPeer.addr.IdentityKey.IsEqual(skip) {
-			srvrLog.Debugf("Skipping %v in broadcast", pubStr)
-			continue
+	for _, sPeer := range s.peersByPub {
+		if skips != nil {
+			if _, ok := skips[sPeer.pubKeyBytes]; ok {
+				srvrLog.Tracef("Skipping %x in broadcast",
+					sPeer.pubKeyBytes[:])
+				continue
+			}
 		}
 
 		// Dispatch a go routine to enqueue all messages to this peer.