wireguard: add WireGuard kernel module and tools

WireGuard is an extremely simple yet fast and modern VPN that utilizes
state-of-the-art cryptography. It aims to be faster, simpler, leaner,
and more useful than IPSec, while avoiding the massive headache.

The recipes add the current experimental snapshot v0.0.20170421
out-of-tree kernel module and tools. The kernel module has some kernel
configuration dependencies such as some configuration part of
features/netfilter/netfilter.scc, hence netfilter.scc should be part
of KERNEL_EXTRA_FEATURES (which is the case by default).

Since wireguard-tools is TUNE_PKGARCH and depends on wireguard-module
which is MACHINE_ARCH (like all kernel modules) we need to add this
dependency to SIGGEN_EXCLUDE_SAFE_RECIPE_DEPS.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>

meta-networking/conf/layer.conf

@@ -21,3 +21,7 @@ LICENSE_PATH += "${LAYERDIR}/licenses"
 
 # Override security flags
 require conf/distro/include/meta_networking_security_flags.inc
+
+SIGGEN_EXCLUDE_SAFE_RECIPE_DEPS += " \
+  wireguard-tools->wireguard-module \
+"