openvpn: update to 2.6.8

openvpn: update to 2.6.8

This is a bugfix release containing security fixes.

Security Fixes (included in 2.6.7):

CVE-2023-46850 OpenVPN versions between 2.6.0 and 2.6.6 incorrectly use a send buffer
after it has been free()d in some circumstances, causing some free()d memory to be sent to the peer.
All configurations using TLS (e.g. not using --secret) are affected by this issue.

CVE-2023-46849 OpenVPN versions between 2.6.0 and 2.6.6 incorrectly restore --fragment configuration
in some circumstances, leading to a division by zero when --fragment is used.
On platforms where division by zero is fatal, this will cause an OpenVPN crash.

For details refer to https://github.com/OpenVPN/openvpn/blob/v2.6.8/Changes.rst

Signed-off-by: Ivan Pavlov <[email protected]>