rework all occurrences of 'M_ERR | M_ERRNO'

rework all occurrences of 'M_ERR | M_ERRNO'

M_ERR is defined as (M_FATAL | M_ERRNO), so 'msg(M_ERR | M_ERRNO, ...)'
is just the same as 'msg(M_ERR, ...)'.

The occurances in tun.c and dco_freebsd.c are really "if this happens,
we can not go on" errors, so 'M_ERR' (= FATAL, plus log errno string)
is the correct thing to do.

The occurances in dns.c do come with error handling and cleanup after
the msg() call, so the right thing is 'M_WARN | M_ERRNO' instead
(warning, plus log errno string).

Github: fixes OpenVPN/openvpn#939

Change-Id: I14395665f197349e374a81b56f28536ff88937a8
Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Arne Schwabe <arne-openvpn@rfc2549.org>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1517
Message-Id: <20260211150648.113547-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg35594.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>