mudp.c: keep offset value when resetting buffer

mudp.c: keep offset value when resetting buffer

dco-win requires control packets to be prepended
with sockaddr. For that, an offset value in buffer
must be kept. Doing it always doesn't harm and makes
code cleaner compared to adding "if (dco_win_server)"
condition.

Change-Id: I145573555aaace5e94774b5f977d032d3747ed72
Signed-off-by: Lev Stipakov <lev@openvpn.net>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20250121161025.37545-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg30519.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>