ovpn-dco: Update to v0.2.20230426

ovpn-dco: Update to v0.2.20230426

OpenVPN 2.6.2+ changes the way OpenVPN control packets are handled on
Linux when DCO is active, fixing the lockups observed with 2.6.0/2.6.1
under high client connect/disconnect activity. This is an INCOMPATIBLE
change and therefore an ovpn-dco kernel module older than v0.2.20230323
(commit ID 726fdfe0fa21) will not work anymore and must be upgraded.
The kernel module was renamed to "ovpn-dco-v2.ko" in order to highlight
this change and ensure that users and userspace software could easily
understand which version is loaded. Attempting to use the old ovpn-dco
with 2.6.2+ will lead to disabling DCO at runtime.

Signed-off-by: Martin Schiller <ms@dev.tdt.de>