init: Use /etc/sysctl.d instead of sysctl.conf

Using a monolithic sysctl.conf makes per-device sysctl overrides difficult
to implement. Switch to using --system which will load all conf files
under /etc/sysctl.d.

CQ-DEPEND=CL:313006
BUG=chromium:555785
TEST=create /etc/sysctl.d on device, move /etc/sysctl.conf into
/etc/sysctl.d/00-sysctl.conf.
reboot and verify sysctl -a shows the same settings as the conf file.

Change-Id: I2f529ae210a3fb7d685714aa08ac0c0d2b51a529
Reviewed-on: https://chromium-review.googlesource.com/313153
Commit-Ready: Stephen Barber <smbarber@chromium.org>
Tested-by: Stephen Barber <smbarber@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/init/chromeos_startup b/init/chromeos_startup
index d7e6b4e..40c2f1b 100755
--- a/init/chromeos_startup
+++ b/init/chromeos_startup
@@ -56,7 +56,7 @@
 
 # Initialize kernel sysctl settings early so that they take effect for boot
 # processes.
-sysctl -q -p /etc/sysctl.conf
+sysctl -q --system
 
 # CROS_DEBUG equals one if we've booted in developer mode or we've
 # booted a developer image.