code: func SubscribeAt(newNs, curNs netns.NsHandle, protocol int, groups ...uint) (*NetlinkSocket, error) {
  	c, err := executeInNetns(newNs, curNs)
  	if err != nil {
  		return nil, err
  	}
  	defer c()
  	return Subscribe(protocol, groups...)
  }
docs: // SubscribeAt works like Subscribe plus let's the caller choose the network
  // namespace in which the socket would be opened (newNs). Then control goes back
  // to curNs if open, otherwise to the netns at the time this function was called.