package/openvpn: bump to version 2.5.0

package/openvpn: bump to version 2.5.0

- Disable unit-tests which are enabled by default if cmocka is found:
  https://github.com/OpenVPN/openvpn/commit/222e691739a111f5becbce39c4cceaa8fff3c284
- Drop --enable-iproute2 to enable netlink(3) support (and so drop
  IFCONFIG, IPROUTE and ROUTE environment variables and keep NETSTAT
  even if it is only used by tests/t_client.sh.in).
  netlink is much faster than calling ifconfig or route and also enables
  OpenVPN to run with less privileges.
- Update indentation in hash file (two spaces)

https://github.com/OpenVPN/openvpn/blob/release/2.5/Changes.rst

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>