ramips: pad EX400 kernel partition to retain web recovery

ramips: pad EX400 kernel partition to retain web recovery

The web-recovery of the Genexis EX400 validates uploaded images to fit
in the rootf_0 partition.

With OpenWrt, only the kernel is stored in this partition, leaving the
partition very small. Currently, the first factory release image won't
be accepted by the recovery interface after the OpenWrt installation.

Pad the image of the ubifs to 10MB. This allows the 24.10 release image
to be uploaded, enabling device recovery.

Signed-off-by: David Bauer <mail@david-bauer.net>
(cherry picked from commit eea4689654e1b07cffe62bc97ad8fef0474bb3b7)