hwcomposer: Clear mVirtualonExtActive on EXTERNAL_OFFLINE

If WFD Client APK is connected and teared down and then hdmi is connecetd
Unblank Virtual display is happening instead of ext display
this results in Display not coming up on External using HDMI.

Change-Id: Id61e9e753f81e90787e2a958f75a4f84b4469f71

Conflicts:
	libhwcomposer/hwc_uevents.cpp