Log serial number of revoked certificate

Log serial number of revoked certificate

As it appears commit 767e4c56becbfeea525e4695a810593f373883cd "Log
serial number of revoked certificate" hasn't survive refactoring
of CRL handling.

In most of situations admin of OpenVPN server needs to know which
particular certificate is used by client.
In the case when certificate is valid, environment variable can be
used for that but once it is revoked, no user scripts are invoked
so there is no way to get serial number, only subject is logged.

Let's log certificate serial in case it is revoked and additionally
log certificate depth & subject in crl-verify "dir" mode for better
consistency with crl file (non-dir) mode.

v2: log if serial is not availble, require it in crl-verify dir mode

Signed-off-by: Vladislav Grishenko <themiron@yandex-team.ru>
Acked-by: Lev Stipakov <lstipakov@gmail.com>
Message-Id: <20200805102333.3109-1-themiron@yandex-team.ru>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg20642.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 992e9cec40539a155afa9eae10502aa62f617965)