powerpc: fix csum_ipv6_magic() on little endian platforms

[Michael Ellerman]

On Mon, 2018-09-10 at 06:09:04 UTC, Christophe Leroy wrote:
> On little endian platforms, csum_ipv6_magic() keeps len and proto in
> CPU byte order. This generates a bad results leading to ICMPv6 packets
> from other hosts being dropped by powerpc64le platforms.
> 
> In order to fix this, len and proto should be converted to network
> byte order ie bigendian byte order. However checksumming 0x12345678
> and 0x56341278 provide the exact same result so it is enough to
> rotate the sum of len and proto by 1 byte.
> 
> PPC32 only support bigendian so the fix is needed for PPC64 only
> 
> Fixes: e9c4943a107b ("powerpc: Implement csum_ipv6_magic in assembly")
> Reported-by: Jianlin Shi <jishi at redhat.com>
> Reported-by: Xin Long <lucien.xin at gmail.com>
> Cc: <stable at vger.kernel.org> # 4.18+
> Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
> Tested-by: Xin Long <lucien.xin at gmail.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/85682a7e3b9c664995ad477520f917

cheers