Merge branch 'sock-netns' of https://github.com/0x7f454c46/util-linux

* 'sock-netns' of https://github.com/0x7f454c46/util-linux:
  lsns: List network namespaces that are held by a socket
  lsfd: Gather information on target socket's net namespace
  nsenter: Provide an option to join target process's socket net namespace

diff --cc configure.ac
Simple merge