wireguard: bump to 0.0.20180809

wireguard: bump to 0.0.20180809

* send: switch handshake stamp to an atomic

Rather than abusing the handshake lock, we're much better off just using
a boring atomic64 for this. It's simpler and performs better. Also, while
we're at it, we set the handshake stamp both before and after the
calculations, in case the calculations block for a really long time waiting
for the RNG to initialize.

* compat: better atomic acquire/release backport

This should fix compilation and correctness on several platforms.

* crypto: move simd context to specific type

This was a suggestion from Andy Lutomirski on LKML.

* chacha20poly1305: selftest: use arrays for test vectors

We no longer have lines so long that they're rejected by SMTP servers.

* qemu: add easy git harness

This makes it a bit easier to use our qemu harness for testing our mainline
integration tree.

* curve25519-x86_64: avoid use of r12

This causes problems with RAP and KERNEXEC for PaX, as r12 is a
reserved register.

* chacha20: use memmove in case buffers overlap

A small correctness fix that we never actually hit in WireGuard but is
important especially for moving this into a general purpose library.

* curve25519-hacl64: simplify u64_eq_mask
* curve25519-hacl64: correct u64_gte_mask

Two bitmath fixes from Samuel, which come complete with a z3 script proving
their correctness.

* timers: include header in right file

This fixes compilation in some environments.

* netlink: don't start over iteration on multipart non-first allowedips

Matt Layher found a bug where a netlink dump of peers would never terminate in
some circumstances, causing wg(8) to keep trying forever. We now have a fix as
well as a unit test to mitigate this, and we'll be looking to create a fuzzer
out of Matt's nice library.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>