Fix STA VLAN bind for RSN pre-authentication case

Fix STA VLAN bind for RSN pre-authentication case

Previously, during RSN preauthentication, ap_sta_bind_vlan() was called,
which fails for non-zero sta->vlan_id as the station is not known to the
kernel driver.

Fix this by binding the station only if it is associated. If it is not
associated, ap_sta_bind_vlan() will be done later during association.

In addition, reject Access-Accept if the returned VLAN ID is not valid
in the current hostapd configuration.

Signed-off-by: Michael Braun <michael-dev@fami-braun.de>