net: sch_generic: fix the missing new qdisc assignment

When commit 2fb541c862c9 ("net: sch_generic: aviod concurrent reset and
enqueue op for lockless qdisc") is backported to stable kernel, one
assignment is missing, which causes two problems reported by Joakim and
Vishwanath, see [1] and [2].

So add the assignment back to fix it.

1. https://www.spinics.net/lists/netdev/msg693916.html .
2. https://www.spinics.net/lists/netdev/msg695131.html

 .

Change-Id: I2e3400f64daa703d44680dedfbd367b152620334
Fixes: 749cc0b0 ("net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc")
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Tested-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Git-Commit: 81504d19
Git-repo: https://android.googlesource.com/kernel/common/


Signed-off-by: Chinmay Agarwal <chinagar@codeaurora.org>