Linux: Retain CAP_NET_ADMIN when dropping privileges

Linux: Retain CAP_NET_ADMIN when dropping privileges

On Linux, when dropping privileges, interaction with
the network configuration, such as tearing down routes
or ovpn-dco interfaces will fail when --user/--group are
used.

This patch sets the CAP_NET_ADMIN capability, which grants
the needed privileges during the lifetime of the OpenVPN
process when dropping root privileges.

Signed-off-by: Timo Rothenpieler <timo@rothenpieler.org>
Reviewed-By: David Sommerseth <davids@openvpn.net>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20220514103717.235-1-timo@rothenpieler.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg24360.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>