dco_linux: extend netlink error cb with extra info

dco_linux: extend netlink error cb with extra info

A netlink error may contain more specific attributes: i.e.
missing attributes or missing neted objects.

Parse and print this information too.

Note that we are re-defining some enum entries that exist
in netlink.h starting with linux-6.1.
Since we do support distros not shipping an up-to-date
netlink.h, we had to re-define the entries we need for
this patch.

Change-Id: I9e27ff335d892429334137d028f8503da4e4ca5b
Signed-off-by: Antonio Quartulli <antonio@mandelbit.com>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20250128134454.2888-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg30658.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>