Linux 4.9 rc4

So it's once again a Saturday afternoon rather than Sunday, this time
because I felt this rc was already big enough.

Part of the size likely comes just from the fact that 4.9 is big and
has some fundamental changes: we have various fixups for drivers and
filesystems that triggered the whole "stack is now viirtually mapped,
and physical addresses don't work" issue.

But a larger part is simply that the first batch of networking fixes
came in just after the rc3 release, which accounts for a large portion
of this rc (about a third in bulk, slightly more in number of commits
- spread out both over network drivers and core networking).

So I'm not going to lie: this is not a small rc, and I'd have been
happier if it was. But it's not unreasonably large for this (big)
release either, so it's not like I'd start worrying. I'm currently
still assuming that we'll end up with the usual seven release
candidates, assuming things start calming down. We'll see how that
goes as we get closer to a release.

Anyway, about half the changes are to drivers (networking being a
notable part of it, but also media and gpu, with misc other noise).
About a third is architecture updates (sparc and mips stand out, but
there's some x86 and parisc too, and some tiny arm updates). The
remainder is mostly core networking, with a smattering of other
changes (filesystems, tests). And Arnd continues to get his
uninitialized variable warning fixes in, so that we hopefully can
re-enable that warning for 4.9 final. Let's see.

The appended shortlog isn't tiny, but you can kind of scan it for an
overview of the kinds of things that happened the past week.