Comment 0 for bug 1238981

[Impact]
Trying to remove a namespace when another namespace is mounted may fail.
Upstream discussion here: http://comments.gmane.org/gmane.linux.network/240795
This affects P/Q/R, but is fixed in S.

[Test Case]
Run this as root in one terminal:

ip netns add netns_one
ip netns add netns_two
ip link add name if_one type veth peer name if_one_peer
ip link add name if_two type veth peer name if_two_peer
ip link set dev if_one_peer netns netns_one
ip link set dev if_two_peer netns netns_two

Run this as root in another terminal:
ip netns delete netns_two

It should pass, but this fails with:
Cannot remove /var/run/netns/netns_two: Device or resource busy

[Fix]
This patch fixes the issue:
https://git.kernel.org/cgit/linux/kernel/git/shemminger/iproute2.git/commit/?id=58a3e8270fe72f8ed92687d3a3132c2a708582dd