code: func (h *Handle) SetNetNsIdByFd(fd, nsid int) error {
  	return h.setNetNsId(NETNSA_FD, uint32(fd), uint32(nsid))
  }
docs: // SetNetNSIdByFd sets the ID of the network namespace for a given fd.
  // fd must be an open file descriptor to a namespace file.
  // The ID can only be set for namespaces without an ID already set.