wireguard: bump to 0.0.20190913

wireguard: bump to 0.0.20190913

Changes since 0.0.20190702:

define conversion constants for ancient kernels
android: refactor and add incoming allow rules
enforce that unused bits of flags are zero
immediately rekey all peers after changing device private key
support running in OpenVZ environments
do not run bc on clean target
skip peers with invalid keys
account for upstream configuration maze changes
openbsd: fix alternate routing table syntax
account for android-4.9 backport of addr_gen_mode
don't fail down when using systemd-resolved
allow specifying kernel release
enforce named pipe ownership and use protected prefix
work around ubuntu breakage
support newer PaX
don't rewrite siphash when it's from compat
squelch warnings for stack limit on broken kernel configs
support rhel/centos 7.7

Signed-off-by: Brandy Krueger <krueger.brandy24@gmail.com>