openvpn: update to 2.4.9

openvpn: update to 2.4.9

This is primarily a maintenance release with bugfixes and improvements.
This release also fixes a security issue (CVE-2020-11810) which allows
disrupting service of a freshly connected client that has not yet
negotiated session keys. The vulnerability cannot be used to
inject or steal VPN traffic.

Release announcement:
https://openvpn.net/community-downloads/#heading-13812
Full list of changes:
https://community.openvpn.net/openvpn/wiki/ChangesInOpenvpn24#OpenVPN2.4.9

Signed-off-by: Magnus Kroken <mkroken@gmail.com>