Kernel version in sources

[remittor]

@gja822

No, I've sysupgraded to my image and got mismatch!

To avoid such problems, you need to do the following things:

1. Build the kernel so that it is binary compatible with official OpenWRT releases:
   https://github.com/openwrt-xiaomi/builder/blob/acd09b1e263f6f382127f6681aa46b643a311e6f/_base.config#L6-L11
2. When building images, you need to patch the vermagic kernel parameter:
   https://github.com/openwrt-xiaomi/openwrt/commit/ffec324c4fce248ced02a9fe6189915a2f5dc75e