Merge iptables at v1.6.1 tag

This pulls in:
  iptables: fix the wrong appending of jump verdict after the comment.
  iptables-save: exit with error if unable to open proc file
  extensions: libxt_rpfilter: add translation to nft
  extensions: libxt_connbytes: Add translation to nft

This is the 'real' upstream iptables 1.6.1

https://git.netfilter.org/iptables/tag/?h=v1.6.1
  commit 7df66f1c
  Author: Shyam Saini <mayhs11saini@gmail.com>
  Committer: Pablo Neira Ayuso <pablo@netfilter.org>

  iptables: fix the wrong appending of jump verdict after the comment.

as opposed to the previous commit we were synced to:
  commit b013e3e8
  Author: Pablo Neira Ayuso <pablo@netfilter.org>
  Date:   Mon Jan 16 14:00:55 2017 +0100

  iptables 1.6.1 release

which merely bumped the version number.

Tested:
  built and flashed to a crosshatch,
  at cursory examination iptables continues to function correctly.

  $ atest netd_unit_test netd_integration_test

  netd_integration_test: Passed: 57, Failed: 0, Ignored: 0
  netd_unit_test: Passed: 164, Failed: 0, Ignored: 0

  All tests passed!

Change-Id: I3e6adff955fc1a8020be5258f2deadd59a4282c5