mediatek: Xiaomi AX3000t: fix soft brick for the rd23 model

mediatek: Xiaomi AX3000t: fix soft brick for the rd23 model

This commit fixes Xiaomi AX3000t soft bricks. Issue affects at least rd23
model (Global version) users:
Link: https://forum.openwrt.org/t/openwrt-support-for-xiaomi-ax3000t/180490/452
I also found that these nvram settings are wrong for the rd23 model and
U-Boot erase them:
'''
flag_try_sys1_failed 8
flag_try_sys2_failed 8
'''
As a result, platform.sh -> xiaomi_initial_setup() function sometimes ends
early without applying settings for the rd23 model.

RD03 model strategy:
1. Don't touch values those were set up by platform.sh ->
xiaomi_initial_setup() function

RD23 model strategy:
1. Apply correct nvram settings at every boot
2. Use bulk fw_setenv call

I didn't find opened issue for AX3000t. Similar AX3200 issue:
Link: https://github.com/openwrt/openwrt/issues/16347
So, other Xiaomi devices (e.g. Xiaomi WR30U) may also require fix.

Fixes: 7dbcc1215a56cc1da68c81bf92d7efa174c5e051 ("mediatek: filogic: add support for Xiaomi AX3000T")
Signed-off-by: Mikhail Zhilkin <csharper2005@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/17580
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>