lxccontainer: only attach netns on netdev detach
lxccontainer: only attach netns on netdev detach

Detaching network namespaces as an unprivileged user is currently not possible
and attaching to the user namespace will mean we are not allowed to move the
network device into an ancestor network namespace.

Signed-off-by: Christian Brauner <48455ab3070520a2d174545c7239d6d0fabd9a83@ubuntu.com>

ss1h2a3tw/lxc,caglar10ur/lxc,hallyn/lxc,caglar10ur/lxc,hallyn/lxc,thmo/lxc,ss1h2a3tw/lxc,thmo/lxc,thmo/lxc,caglar10ur/lxc,ss1h2a3tw/lxc,hallyn/lxc