func (t *Transport) ActivePeers() (cnt int) {
	t.mu.RLock()
	defer t.mu.RUnlock()
	for _, p := range t.peers {
		if !p.activeSince().IsZero() {
			cnt++
		}
	}
	return cnt
}
func (t *Transport) ActivePeers() (cnt int) {
	t.mu.RLock()
	defer t.mu.RUnlock()
	for _, p := range t.peers {
		if !p.activeSince().IsZero() {
			cnt++
		}
	}
	return cnt
}
// ActivePeers returns a channel that closes when an initial
// peer connection has been established. Use this to wait until the
// first peer connection becomes active.