When using IEEE 802.11r FT OVER-DS roaming with AP_VLAN, hostapd needs to
send out a frame using CMD_FRAME for a station assigned to an AP_VLAN
interface.

Right now, the userspace needs to give the exact AP_VLAN interface index
for CMD_FRAME; hostapd does not do this. Additionally, userspace cannot
use GET_STATION to query the AP_VLAN ifidx, as while GET_STATION finds
stations assigned to AP_VLAN even if the AP iface is queried, it does not
return AP_VLAN ifidx (it returns the queried one).

This breaks IEEE 802.11r over_ds with vlans, as the reply frame does not
get out. This patch fixes this by using get_sta_bss for CMD_FRAME.
Signed-off-by: Michael Braun <michael-dev@fami-braun.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>