Fix STA re-bind to another VLAN on reauthentication

Fix STA re-bind to another VLAN on reauthentication

Previously, the old VLAN ID could have been deleted before the STA was
bound to the new VLAN in case the RADIUS server changed the VLAN ID
during an association. This did not exactly work well with mac80211, so
reorder the operations in a way that first binds the STA to the new VLAN
ID and only after that, removes the old VLAN interface if no STAs remain
in it.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>