net: skbuff: disambiguate argument and member for skb_list_walk_safe helper

stable inclusion
from linux-4.19.170
commit bae6277ad341d4fbfa564409c310bd151f235250

--------------------------------

commit 5eee7bd7 upstream.

This worked before, because we made all callers name their next pointer
"next". But in trying to be more "drop-in" ready, the silliness here is
revealed. This commit fixes the problem by making the macro argument and
the member use different names.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>