Request to cherry-pick 3db09e762dc7 to 4.14+

Hi all,

Commit 3db09e762dc79584a69c10d74a6b98f89a9979f8 upstream ("net/sched: cls_u32: fix netns refcount changes in u32_change()") fixes a crash and seems like a good candidate for stable trees.

The change fixes 35c55fc156d8 ("cls_u32: use tcf_exts_get_net() before call_rcu()"), which was added in 4.14, so I think it might make sense to cherry-pick the fix to 4.14+.

Let me know what you think.

Thanks, -Robert