datapath: use skb_list_walk_safe helper for gso segments

datapath: use skb_list_walk_safe helper for gso segments

Upstream commit:
    commit 2cec4448db38758832c2edad439f99584bb8fa0d
    Author: Jason A. Donenfeld <Jason@zx2c4.com>
    Date:   Mon Jan 13 18:42:29 2020 -0500

    net: openvswitch: use skb_list_walk_safe helper for gso segments

    This is a straight-forward conversion case for the new function, keeping
    the flow of the existing code as intact as possible.

    Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Yi-Hung Wei <yihung.wei@gmail.com>
Signed-off-by: Greg Rose <gvrose8192@gmail.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>