Don't mark wifi disabled unless it's off.

The transition from driver-started to scan-only state was incorrectly
always marking wifi disabled, but transitioning back only marked it
enabled if we were exiting due to leaving the scan-only-with-wifi-off
mode.

bug:11062188
Change-Id: I44fe64fd8dac8f36f4e22cb1c16b9d7a06bdbac0