dco-linux: remove M_ERRNO flag when printing netlink error message

dco-linux: remove M_ERRNO flag when printing netlink error message

Netlink has its own error space and reports errors via the return
value of its functions.

For this reason remove the M_ERRNO flag when printing its errors.
At the moment we get something like this:

netlink reports error (-7): Invalid input data or parameter: Interrupted
system call (errno=4)

where the errno=4 (and its human readable representation) is a leftover
from the previous recv() interrupted by a signal and it is totally
unrelated to this netlink failure.

Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20230320195820.6675-1-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26452.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 23903fd579353c9892415a750f17a9832a79cced)