The Group ID Management frame is an Action frame of category VHT.
It is transmitted by the AP to assign or change the user position
of a STA for one or more group IDs.

Also, sniffer can use a given group id to monitor STA that belongs
to that group.

Notify underlying driver of changes via BSS_CHANGED_MU_GROUPS.
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>