Sent indication that a session is expired to clients

Sent indication that a session is expired to clients

This allows OpenVPN 3 core to fall back to the original authentication
method.

This commit changes man_def_auth_set_client_reason to
auth_set_client_reason since it now used in more contexts.

Also remove a FIXME about client_reason not being freed, as it is freed
in tls_multi_free with auth_set_client_reason(multi, NULL);

Patch V4: Rebase on master
Patch V7: Rebase on master
Acked-by: David Sommerseth <davids@openvpn.net>
Message-Id: <20190917121115.13966-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg18820.html

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