Zyxel NBG6716 support

[Alex Henrie]

Hello,

I have a Zyxel NBG6716 that was running OpenWrt 19.07, but when I
upgraded it to OpenWrt 21.02 it stopped booting. The serial console,
the bootloader, and the bootloader's TFTP command still work though. I
found a note in the Git logs that says that the OpenWrt kernel is now
too big for this device.[1] Is anyone interested in trying to restore
OpenWrt support for the NBG6716? In the end I just bought a different
router, so I'd be happy to send you the borked one if you want to work
on it.

-Alex

[1] https://git.openwrt.org/?p=openwrt/openwrt.git;a=commitdiff;h=5d8ea6d34f9f23d4dfff4ffcac8c9599d842c3a8