system_api: change variable names for "SSID" feature to "DarkConnect"

Change variable names so that the wake on WiFi "SSID" feature is
now known as "DarkConnect".

BUG=chromium:431486
CQ-DEPEND=CL:307923
TEST=None

Change-Id: Icc3a4ea291f788d48bff0799312740e2cad9bf53
Reviewed-on: https://chromium-review.googlesource.com/307103
Commit-Ready: Samuel Tan <samueltan@chromium.org>
Tested-by: Samuel Tan <samueltan@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
1 file changed