Option to set interface to 4-addr mode

[Konstantinos Natsakis]

Hello,

Would you be interested in a patch for wpa_supplicant that adds a new 
command line option to set an interface to 4-address mode?

Does it make more sense, perhaps, to always set an interface to 4-addr 
mode when the `-b` option is present?

Some context: I did some work on 
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/1330 
(Support setting 4-addr (WDS) mode per WiFi connection), and it was 
suggested that wpa_supplicant should handle setting 4-addr mode of the 
interface, which I too think make sense.

Any feedback is appreciated.

Regards,

Konstantinos