Disassociate when starting WPS search
Previously, the WPS scans could have been done in associated state if we
happened to be associated when the request to use WPS was received. This
can slow down scanning and end up in unexpected state if no WPS
association is tried. Avoid these issues by disconnecting when WPS
search is started.
Signed-hostap: Jouni Malinen <j@w1.fi>