In case there are more `user` network interfaces defined, allow to
specific the netdev. If omitted, an empty string is passed and the
behaviour is like before.

This is useful for testing OpenWrt inside a QEMU instance, since OpenWrt
expects by default a LAN interface on eth0 and a WAN interface (with
uplink) on eth1. Previously the port forward would always be added to
eth1, which doesn't support SSH due to firewall policies. By adding the
netdev to the forward function, the SSHDriver works as expected.

Signed-off-by: Paul Spooren <mail@aparcar.org>

Using PoE switches as power supply is convenient since a switch is
needed in many cases anyway and with the right adapter most embedded
devices can be powered.

OpenWrt offers `ubus` as micro bus system to control the system,
including PoE ports on switches.

This commit adds a driver to handle PoE switches running OpenWrt.

Signed-off-by: Paul Spooren <mail@aparcar.org>