wireguard: bump to 0.0.20180918

wireguard: bump to 0.0.20180918

* blake2s-x86_64: fix whitespace errors
* crypto: do not use compound literals in selftests
* crypto: make sure UML is properly disabled
* kconfig: make NEON depend on CPU_V7
* poly1305: rename finish to final
* chacha20: add constant for words in block
* curve25519-x86_64: remove useless define
* poly1305: precompute 5*r in init instead of blocks
* chacha20-arm: swap scalar and neon functions
* simd: add __must_check annotation
* poly1305: do not require simd context for arch
* chacha20-x86_64: cascade down implementations
* crypto: pass simd by reference
* chacha20-x86_64: don't activate simd for small blocks
* poly1305-x86_64: don't activate simd for small blocks
* crypto: do not use -include trick
* crypto: turn Zinc into individual modules
* chacha20poly1305: relax simd between sg chunks
* chacha20-x86_64: more limited cascade
* crypto: allow for disabling simd in zinc modules
* poly1305-x86_64: show full struct for state
* chacha20-x86_64: use correct cut off for avx512-vl
* curve25519-arm: only compile if symbols will be used
* chacha20poly1305: add __init to selftest helper functions
* chacha20: add independent self test

Tons of improvements all around the board to our cryptography library,
including some performance boosts with how we handle SIMD for small packets.

* send/receive: reduce number of sg entries

This quells a powerpc stack usage warning.

* global: remove non-essential inline annotations

We now allow the compiler to determine whether or not to inline certain
functions, while still manually choosing so for a few performance-critical
sections.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
(backported from f07a94da50b8a31928cb34c19695747e0df74beb)