OpenWrt完美扩容Overlay 硬核新方法，真扩容，零空间浪费！
直接扩容镜像
解压
gzip -kd openwrt-spp-winter[2022]-x86-64-generic-squashfs-legacy.img.gz
改名
mv openwrt-spp-winter[2022]-x86-64-generic-squashfs-legacy.img.gz op.img
扩容500M
dd if=/dev/zero bs=1M count=500 >> op.img
parted op.img
print
resizepart 2 100%
quit