mac80211: fix wext bssid/ssid setting

mac80211: fix wext bssid/ssid setting

When changing to a new BSSID or SSID, the code in
ieee80211_set_disassoc() needs to have the old data
still valid to be able to disconnect and clean up
properly. Currently, however, the old data is thrown
away before ieee80211_set_disassoc() is ever called,
so fix that by calling the function _before_ the old
data is overwritten.

This is (one of) the issue(s) causing mac80211 to hold
cfg80211's BSS structs forever, and them thus being
returned in scan results after they're long gone.

http://www.intellinuxwireless.org/bugzilla/show_bug.cgi?id=2015

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>