Bump version of openvpn plugin argument structs to 5

Bump version of openvpn plugin argument structs to 5

This was missed in commit 6690769f78bbfb889fef2a54088d979896c87d51
that exported base64_encode and base64_decode() functions.

Also check the version is >= 5 in auth-pam plugin to ensure
that the base64_decode function pointer can be referenced.

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1533696271-21799-1-git-send-email-selva.nair@gmail.com>
URL: https://www.mail-archive.com/search?l=mid&q=1533696271-21799-1-git-send-email-selva.nair@gmail.com
Signed-off-by: Gert Doering <gert@greenie.muc.de>