tests: Verify correct VLAN operation in multi-BSS multi-VLAN case

tests: Verify correct VLAN operation in multi-BSS multi-VLAN case

This adds hwsim test ap_vlan_iface_cleanup_multibss. It connects two
stations in different BSS but the same hostapd process. First both
stations are in VLAN 1, then they get reauthenticated into VLAN 2. Due
to the ordering of the stations moving around, this test checks that
bridge and tagged interface referencing counting is done globally, such
that the tagged interface is not removed too early and no bridge is
left over.

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