reload CRL only if file was modified

reload CRL only if file was modified

In order to prevent annoying delays upon client connection,
reload the CRL file only if it was modified since the last
reload operation.
If not, keep on using the already stored CRL.

This change will boost client connection time in instances
where the CRL file is quite large (dropping from several
seconds to few milliseconds).

Cc: Steffan Karger <steffan.karger@fox-it.com>
Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <20161201104145.23821-1-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg13345.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>