wireguard: bump to 20180420

wireguard: bump to 20180420

7cc2668 version: bump snapshot
860c7c7 poly1305: do not place constants in different sections
5f1e4ca compat: remove unused dev_recursion_level backport
7e4b991 blake2s: remove unused helper
13225fc send: simplify skb_padding with nice macro
a1525bf send: account for route-based MTU
bbb2fde wg-quick: account for specified fwmark in auto routing mode
c452105 qemu: bump default version
dbe5223 version: bump snapshot
1d3ef31 chacha20poly1305: put magic constant behind macro
cdc164c chacha20poly1305: add self tests from wycheproof
1060e54 curve25519: add self tests from wycheproof
0e1e127 wg-quick.8: fix typo
2b06b8e curve25519: precomp const correctness
8102664 curve25519: memzero in batches
1f54c43 curve25519: use cmov instead of xor for cswap
fa5326f curve25519: use precomp implementation instead of sandy2x
9b19328 compat: support OpenSUSE 15
3102d28 compat: silence warning on frankenkernels
8f64c61 compat: stable kernels are now receiving b87b619
62127f9 wg-quick: hide errors on save

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>