code: func (ln *LocalNode) SetFallbackIP(ip net.IP) {
  	ln.mu.Lock()
  	defer ln.mu.Unlock()
  
  	ln.fallbackIP = ip
  	ln.updateEndpoints()
  }
docs: // SetFallbackIP sets the last-resort IP address. This address is used
  // if no endpoint prediction can be made and no static IP is set.