kernel/linux: fix packed attribute in exported headers

UBI headers (and maybe others as well) are broken because the 'packed'
attribute is not sanitised when the headers are exported to userspace.

Apply the fix from upstream:
https://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=f210735fe2f17a6225432ee3d1239bcf23a8659c

(Also, buildroot does the same, BTW)

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 # Bare metal config options

 ## select BARE_METAL

 ##

 ## help 'Bare metal' refers to those programs that run without any kernel.

 ## help

 ## help You probably want to say 'y' here if you plan to use your compiler

 ## help to build bootloaders. It is not yet suitable to build Linux kernels,

 ## help though, because the APCI stuff relies on the target C library headers

 ## help being available?!?!...