Delay scan request on select_network if disconnecting

Delay scan request on select_network if disconnecting

The disconnection command results in disassociation and deauthentication
events which were previously processed during the scan in case of
select_network command being used while associated with another network.
While this works in most cases, it can result in confusing event
messages in ctrl_iface and debug log. Avoid this by using a short delay
between the disconnection and scan request to allow the disconnection
events to be processed prior to starting the new scan.

Signed-hostap: Jouni Malinen <j@w1.fi>
intended-for: hostap-1