Merge branch 'lsfd--socknetns-for-tuntap' of https://github.com/masatake/util-linux

Merge branch 'lsfd--socknetns-for-tuntap' of https://github.com/masatake/util-linux

* 'lsfd--socknetns-for-tuntap' of https://github.com/masatake/util-linux:
  lsfd: fill SOCK.NETNS column for tuntap
  lsfd: load the information of the network namespace behind a tun device
  lsfd: (refactor) call ioctl(TUNGETDEVNETNS) from target_fd related methods
  lsfd: add stubs of target_fd related methods to cdev_class
  tests: (lsfd::*) revise the way to use "$?"
  tests: (lsns::*) revise the way to use "$?"