Merge branch 'test_mkfds-sockdiag-for-master' of https://github.com/masatake/util...

Merge branch 'test_mkfds-sockdiag-for-master' of https://github.com/masatake/util-linux

* 'test_mkfds-sockdiag-for-master' of https://github.com/masatake/util-linux:
  tests: (test_mkfds::sockdiag) verify the recieved message to detect whether the socket is usable or not
  lsfd: add LSFD_DEBUG env var for debugging
  tests: (lsfd) skip some cases if NETLINK_SOCK_DIAG for AF_UNIX is not available
  tests: (test_mkfds::sockdiag) new factory
  tests: (lsfd-functions.bash,cosmetic) unify the style to define functions
  tests: (lsfd) fix typoes in an error name