don't broadcast-gossip other peer when adding a connection

This is more efficient since broadcasting about other peers is
strictly redundant. Any change to the peers will be broadcast by
those peers anyway. And SendAllGossipDown takes care of informing new
peers about others on first connect, and periodic gossip take care of
missed broadcasts.

The only reason we did broadcast about the remote peer is to reduce
the liklihood of UnknownPeerError and the associated throwing away of
gossip. This was always a bit of kludge, and is no longer necessary
since UnknownPeerError is gone.

Now peers only ever broadcast information about themselves. Which,
unlike information about other peers, is always authorative and most
up-to-date. Which is nice.

mesh/local_peer.go

@@ -157,7 +157,7 @@ func (peer *LocalPeer) handleAddConnection(conn Connection) error {
 	}
 
 	peer.router.Routes.Recalculate()
-	peer.broadcastPeerUpdate(conn.Remote())
+	peer.broadcastPeerUpdate()
 
 	return nil
 }
@@ -199,13 +199,13 @@ func (peer *LocalPeer) handleDeleteConnection(conn Connection) {
 
 // helpers
 
-func (peer *LocalPeer) broadcastPeerUpdate(peers ...*Peer) {
+func (peer *LocalPeer) broadcastPeerUpdate() {
 	// Some tests run without a router.  This should be fixed so
 	// that the relevant part of Router can be easily run in the
 	// context of a test, but that will involve significant
 	// reworking of tests.
 	if peer.router != nil {
-		peer.router.BroadcastTopologyUpdate(append(peers, peer.Peer))
+		peer.router.BroadcastTopologyUpdate([]*Peer{peer.Peer})
 	}
 }