t_net.sh: delete dummy iface using iproute command

t_net.sh: delete dummy iface using iproute command

A dummy interface cannot be deleted using --rmtun because openvpn tries
to send some ioctl (i.e. TUNSETPERSIST) which is not supported by this
device type. This results in the following error:

2022-04-07 09:59:29 Cannot ioctl TUNSETPERSIST(0) ovpn-dummy0: Bad file
descriptor (errno=9)
2022-04-07 09:59:29 Exiting due to fatal error

and the interface is not deleted.

Use iproute to generically delete an interface.

Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20220407081555.25228-1-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg24086.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>