Revert "Update 99-default_network"

This reverts commit 8b2e69c4c2.

root/package/base-files/files/etc/board.d/99-default_network

@@ -1,3 +1,4 @@
+#!/bin/sh
 #
 # Copyright (C) 2013-2015 OpenWrt.org
 #
@@ -9,8 +10,7 @@ board_config_update
 json_is_a network object && exit 0
 
 ucidef_set_interface_lan 'eth0'
-[ -d /sys/class/net/eth1 ] && ucidef_set_interface_wan 'eth1'
 
 board_config_flush
 
-exit 0
+exit 0