Document/cleanup event_timeout functions

Document/cleanup event_timeout functions

Remove function event_timeout_clear_ret as it is unused.

Cleanup event_timeout_trigger a bit. Do an instant return false if the
timeout is not defined and inline local_now and use
event_timeout_remaining instead of local duplicated code.

Add doxygen comments for all timeout function, especially for the
event_timeout_trigger function that is hard to understand otherwise.

Patch v2: add many fixes/correction suggested by Frank

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20221006122940.1202712-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg25348.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>