Del ipv6 addr on close of linux tun interface

Del ipv6 addr on close of linux tun interface

When a linux tun interface is closed (e.g. on disconnect)
an optional ipv6 addr that was previously set is deleted now.
Without this patch a later reconnect could fail with
'Linux ip -6 addr add failed: external program exited with error status: 2'
and openvpn would exit.

This is mainly relevant for persistant tun devices (staying around
after openvpn exits) but can also happen at reconnect.

If addresses are *supposed* to stay around on openvpn exit, run
openvpn with --ifconfig-noexec and configure IPv4/IPv6 addresses
manually before openvpn starts (or using an --up script).

Trac #141

Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1435248080-12670-1-git-send-email-Holger.Kummert@Sophos.com>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9810

Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit e5f71d674e3b119d6a252d7cef1c17b5c2b36a9a)