Linux 4.15 rc9

I really really wanted to just release 4.15 today, but things haven't
calmed down enough for me to feel comfy about it, and Davem tells me
he still has some networking fixes pending. Laura Abbott found and
fixed a very subtle boot bug introduced this development cycle only
yesterday, and it just didn't feel right to say that we're done.

So I'm doing an rc9 instead. I don't particularly like to, but I like
it even less releasing something that doesn't seem baked enough.

Some people have already started sending me pull requests for 4.16
(generally because they aren't expecting to be online next week and
expected the merge window to open). I appreciate it, and I'll keep
them queued up, I just won't start applying them quite yet.

Anyway, rc9 is mostly arch updates (x86, arm, powerpc, mips) and
drivers (gpu, networking and md). And some core networking. And then
there's various random misc fallout (tracing, bpf, and new selftests)

I really expect no more delays after this. We've had rc9's before, but
they have been pretty rare (the last one was 3.1-rc9 back in 2011 -
that release went all the way to rc10, and I really don't think we'll
do that this time _despite_ all the CPU bug mitigation craziness).