The stock firmware and bootloader only accept uImage with names that
match certain patterns. This patch enables OpenWrt installation from
stock firmware without having to reflash the bootloader or access the
UART console.

Installation via web interface:
1.  Flash **initramfs** image through the stock web interface.
2.  Boot into OpenWrt and perform sysupgrade with sysupgrade image.

Signed-off-by: Sungbo Eo <mans0n@gorani.run>
(cherry picked from commit 19800ac0

)
[backported]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>