oxnas: set preinit network interface

set network interface for failsafe mode to eth0 for all boards

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

target/linux/oxnas/base-files/lib/preinit/07_set_preinit_iface_oxnas.sh

+#!/bin/sh
+
+oxnas_set_preinit_iface() {
+	ifname=eth0
+}
+
+boot_hook_add preinit_main oxnas_set_preinit_iface