Fix '--inactive <time> 0' behavior for DCO

Fix '--inactive <time> 0' behavior for DCO

Make sure we exit if <bytes> is 0 (not set) and no traffic
was produced.

According to man page and non-DCO --inactive implementation,
we exit if amount of bytes produced is less than <bytes> specified.
DCO implementation will do off-by-ones, but we consider it as okay
since we don't want to complicate code to handle both bytes=0 and >0
cases.

Change-Id: I4c089e486728a43bfe42596787c00355838311da
Signed-off-by: Lev Stipakov <lev@openvpn.net>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20230322113408.2057-1-lstipakov@gmail.com>
URL: https://www.mail-archive.com/search?l=mid&q=20230322113408.2057-1-lstipakov@gmail.com
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 6c64b46b15476351ca19f9a8f3cb8185aa2c7e07)