Allow interface names to change on updates to handle hwconfig -> DSA and
similar migrations.
On devices with only a single interface, a sysconfig single_ifname is
created instead of wan_ifname or lan_ifname to allow separate
configuration in site.conf.
On PoE-powered devices, we usually want to use WAN for the setup mode.
As all outdoor devices are PoE-powered, we can reuse this function. This
switches the setup mode interface for new installations / after config
reset on a few devices that were missing in this list before.
