wlan: Disassoc peers in SAP mode during stop adapter

If delete interface is called for SAP directly without, calling
stop ap, driver doesn't send unicast disassoc frame to AP.
In this case driver send the BC disassoc frame, which may be missed
by peer.

So from stop adapter delete all the connected peers by sending
unicast disassoc frames.

Change-Id: Ideefbca5b250a24e29b66122fd32019cf7441f30
CRs-Fixed: 2449739