Initially there were no peers connected to AP VDEV when the VDEV was in
MLO_SYNC_WAIT state. So EV_DOWN would directly move to STOP state and
proceed with bringing down the vdev.
With CSA in MLO, there can peers connected to AP VDEV in MLO_SYNC_WAIT
which have to be deleted/cleaned up as part EV_DOWN event handling.
Added change to handle the DOWN event as done in START/UP_ACTIVE state.
By moving to SUSPEND, the clients are disconnected then moving to
STOP state.
Change-Id: Ida71914b9719395ab666805cc7072491ffa9baf1
CRs-Fixed: 3308207
f724435caa