dco-linux: fix counter print format

dco-linux: fix counter print format

Avoid compilation warnings on 32 bit platforms.

dco_linux.c: In function 'dco_update_peer_stat':
dco_linux.c:830:26: error: format '%lu' expects argument of type
'long unsigned int', but argument 4 has type 'counter_type'
{aka 'long long unsigned int'} [-Werror=format=]
  830 |         msg(D_DCO_DEBUG, "%s / dco_read_bytes: %lu", __func__,
      |                          ^~~~~~~~~~~~~~~~~~~~~~~~~~
  831 |             c2->dco_read_bytes);
      |             ~~~~~~~~~~~~~~~~~~
      |               |
      |               counter_type {aka long long unsigned int}

Signed-off-by: Sergey Korolev <sergey.korolev@keenetic.com>
Acked-by: Antonio Quartulli <a@unstable.cc>
Message-Id: <20230626130939.3267280-1-sergey.korolev@keenetic.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26767.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>