wireguard: bump to 0.0.20180625

wireguard: bump to 0.0.20180625

dfd9827 version: bump snapshot
88729f0 wg-quick: android: prevent outgoing handshake packets from being dropped
1bb9daf compat: more robust ktime backport
68441fb global: use fast boottime instead of normal boottime
d0bd6dc global: use ktime boottime instead of jiffies
18822b8 tools: fix misspelling of strchrnul in comment
0f8718b manpages: eliminate whitespace at the end of the line
590c410 global: fix a few typos
bb76804 simd: add missing header
7e88174 poly1305: give linker the correct constant data section size
fd8dfd3 main: test poly1305 before chacha20poly1305
c754c59 receive: don't toggle bh

Compile-tested-for: ath79 Archer C7 v2
Run-tested-on: ath79 Archer C7 v2

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
(cherry picked from commit 3ce11588f6346ebedde68ef30a06e01999e292bb)