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
TEST=Manually test that wake on WiFi features still work as expected.

Review URL: https://codereview.chromium.org/1412993003

Cr-Commit-Position: refs/heads/master@{#356622}
15 files changed