VLAN: Separate station grouping and uplink configuration

VLAN: Separate station grouping and uplink configuration

Separate uplink configuration (IEEE 802.1q VID) and grouping of stations
into AP_VLAN interfaces.

The int vlan_id will continue to identify the AP_VLAN interface the
station should be assigned to. Each AP_VLAN interface corresponds to an
instance of struct hostapd_vlan that is uniquely identified by int
vlan_id within an BSS.

New: Each station and struct hostapd_vlan holds a struct
vlan_description vlan_desc member that describes the uplink
configuration requested. Currently this is just an int untagged IEEE
802.1q VID, but can be extended to tagged VLANs and other settings
easily.

When the station was about to be assigned its vlan_id, vlan_desc and
vlan_id will now be set simultaneously by ap_sta_set_vlan(). So
sta->vlan_id can still be tested for whether the station needs to be
moved to an AP_VLAN interface.

To ease addition of tagged VLAN support, a member notempty is added to
struct vlan_description. Is is set to 1 if an untagged or tagged VLAN
assignment is requested and needs to be validated. The inverted form
allows os_zalloc() to initialize an empty description.

Though not depended on by the code, vlan_id assignment ensures:
  * vlan_id = 0 will continue to mean no AP_VLAN interface
  * vlan_id < 4096 will continue to mean vlan_id = untagged vlan id
    with no per_sta_vif and no extra tagged vlan.
  * vlan_id > 4096 will be used for per_sta_vif and/or tagged vlans.

This way struct wpa_group and drivers API do not need to be changed in
order to implement tagged VLANs or per_sta_vif support.

DYNAMIC_VLAN_* will refer to (struct vlan_description).notempty only,
thus grouping of the stations for per_sta_vif can be used with
DYNAMIC_VLAN_DISABLED, but not with CONFIG_NO_VLAN, as struct
hostapd_vlan is still used to manage AP_VLAN interfaces.

MAX_VLAN_ID will be checked in hostapd_vlan_valid and during setup of
VLAN interfaces and refer to IEEE 802.1q VID. VLAN_ID_WILDCARD will
continue to refer to int vlan_id.

Renaming vlan_id to vlan_desc when type changed from int to struct
vlan_description was avoided when vlan_id was also used in a way that
did not depend on its type (for example, when passed to another
function).

Output of "VLAN ID %d" continues to refer to int vlan_id, while "VLAN
%d" will refer to untagged IEEE 802.1q VID.

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