Comment 6 for bug 1672144

It works on linux 4.11-rc3.
After kernel bisect, this commit fixes the issue:

commit 91864f5852f9996210fad400cf70fb85af091243
Author: Andrey Vagin <email address hidden>
Date: Sun Mar 12 21:36:18 2017 -0700

    net: use net->count to check whether a netns is alive or not

    The previous idea was to check whether a net namespace is in
    net_exit_list or not. It doesn't work, because net->exit_list is used in
    __register_pernet_operations and __unregister_pernet_operations where
    all namespaces are added to a temporary list to make cleanup in a error
    case, so list_empty(&net->exit_list) always returns false.

    Reported-by: Mantas Mikulėnas <email address hidden>
    Fixes: 002d8a1a6c11 ("net: skip genenerating uevents for network namespaces that are exiting")
    Signed-off-by: Andrei Vagin <email address hidden>
    Signed-off-by: David S. Miller <email address hidden>

And it's also included in 4.10.5 stable tree, so it'll land to 17.04's linux kernel soon.
You can try 4.10.5 mainline kernel at here:
  http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.10.5/