dco: add standard mi prefix handling to multi_process_incoming_dco()

dco: add standard mi prefix handling to multi_process_incoming_dco()

Our code generally expects functions that deal with a multi instance
to set up a log prefix at the beginning with set_prefix(mi) and clear
it at the end with clear_prefix().

Add the calls to multi_process_incoming_dco() in a similar way to
what is done for multi_process_incoming_link() - handling "link
events" and "dco events" the same, with correct prefix in the
function and no leftover prefix afterwards.

Github: closes OpenVPN/openvpn#799
Change-Id: I1ad5df0f6785ffe9becd9f83329a9335d1a36f24
Signed-off-by: Antonio Quartulli <antonio@mandelbit.com>
Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20250911201222.25382-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg32859.html
URL: https://gerrit.openvpn.net/c/openvpn/+/1116
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 531fef40b73f73632548c88697af34cf15a70531)