Feature request, limit the max stations for each psk key

[Mohammad Rasim]

Hi,

It would be useful if we can configure the max station number allowed to 
connect per psk.

one could use "max_num_sta" as a global setting for maximum number of 
clients, but i want to limit the connected clients per psk key when 
using wpa_psk_file.

it could be defined in the wpa_psk_file for each psk for example:

`max_num_sta=1 keyid=first 00:00:00:00:00:00 12345678`

or as a global setting for example in hostapd.conf:

`max_num_sta_per_psk=1`

which will limit each psk to be used simultaneously by only one client.

it could be implemented like so:

when a client tries to connect and hostapd is looping through the psks 
from the wpa_psk_file it should check for the connected clients and see 
how many clients are connected using the psk (it could be identified by 
using the keyid for example) and if the connected clients is equal to 
the "max_num_sta_per_psk" setting then it should not use that psk and 
tries the next one instead.


Regards