nitrogen6x: supply custom version of /etc/network/interfaces

Nitrogen6X/6_Max/6_Lite all use the nl80211 driver for wpa_supplicant
and none of them have an eth1 device.

Change-Id: I17a316d79a1d787229fd9acb758d993921e85dfb
Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@digia.com>