use system virtwl header

Use the system-install virtwl header. In CrOS, this is installed in the
sys-kernel/linux-headers package.

BUG=chromium:826923
TEST=emerge vm_guest_tools

Change-Id: I5ba6acdc6cae77084f803d7d01592ffc02baf324
Reviewed-on: https://chromium-review.googlesource.com/997181
Tested-by: Stephen Barber <smbarber@chromium.org>
Reviewed-by: David Reveman <reveman@chromium.org>
3 files changed