dco_linux: enable extended netlink error reporting

dco_linux: enable extended netlink error reporting

The ovpn netlink code reports more verbose error
strings to help userspace understand what went wrong,
rather than just returning, for example, -EINVAL.

However, userspace must instruct the kernel netlink
subsystem that it wants to receive such strings.

code for parsing such strings has always been present
but it was never used.

Set the socket option which enables such reporting.

Change-Id: I4457b1d7262e0a39c275d33aaef6c4bcbeae6ab3
Signed-off-by: Antonio Quartulli <antonio@mandelbit.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20250609100216.3997-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg31885.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>