Use undo_lists for saving ring-buffer handles in interactive service

Use undo_lists for saving ring-buffer handles in interactive service

HandleRegisterRingBuffers() in interactive.c did not follow the
the original API of HandleMessage(): a new argument was added
to HandleMessage to pass-in prer-process ring-buffer handles. The
existing undo lists argument is meant for such use.

Rewrite following the original design.

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Lev Stipakov <lstipakov@gmail.com>
Message-Id: <20221229182739.1477336-1-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg25864.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 6ea9cf8146b1d72aa6a4790bc3ac2b99562b2cac)