Merge branch 'lsfd--misc-tun' of https://github.com/masatake/util-linux

Merge branch 'lsfd--misc-tun' of https://github.com/masatake/util-linux

* 'lsfd--misc-tun' of https://github.com/masatake/util-linux:
  tests: (lsfd) add a case testing TUN.IFACE column
  tests: (mkfds) add a factor for opening tun device
  lsfd: add TUN.IFFACE, a column for interfaces behind tun devices
  lsfd: (refactor) move miscdev specific code to cdev_misc_ops
  lsfd: (refactor) make the way to handle character devices extensible
  lsfd: (refactor) introduce a content data type for char devices