Linux 4.9 rc6

We're getting further in the rc series, and while things have stayed
pretty calm, I'm not sure if we're quite there yet. There's a few
outstanding issues that just shouldn't be issues at rc6 time, so we'll
just have to see. This may be one of those releases that have an rc8,
which considering the size of 4.9 is perhaps not that unusual.

That said, nothing particular is bothering me all that much, but we've
had some of the VMALLOC_STACK fixups continue to trickle in, so I
worry that we're not quite done there yet. And let's see what
Thorsten's regression list looks like next week. So no decision yet,
it could still go either way.

The fact that rc6 is bigger than rc5 was is not a particularly great
sign, though. But most of that seems to be just the usual timing
fluctuation: rc6 had networking updates, rc5 didn't, for example.
There are also some rdma updates etc that stand out. Nothing that
looks particularly worrisome.

Aside from the aforementioned networking and rdma, there's gpu fixes,
some tooling and build fixes, and various arch updates (x86, powerpc,
arm, xtensa). And misc fixes all over (i2c, sound, fuse, kvm..)

Go forth and test,