dco: turn platform config checks into separate function

dco: turn platform config checks into separate function

All the checks in there are only relevant during startup, and
specifically the capability check might cause issues when checking a CCD
config later at runtime.

So move them to their own function and call it only during startup.
Acked-by: Antonio Quartulli <a@unstable.cc>
Message-Id: <20220817210857.1558-1-timo@rothenpieler.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg24969.html

Signed-off-by: Gert Doering <gert@greenie.muc.de>