qtnfmac: add support for 4addr mode

Advertise WIPHY_FLAG_4ADDR_STATION capability to wireless core. Send
use4addr interface change flag to firmware in change_virtual_intf
cfg80211 callback.

In order to enable adding wireless station interface to bridge
one should turn on 4addr mode using the following command:
$ iw dev wlan0 set 4addr on
$ brctl addif br0 wlan0

If this commands succeeds, then interface can be added to bridge.
Note that when wireless interface is added to bridge, wpa_supplicant
should be started with appropriate -b <brname> parameter, e.g:
$ wpa_supplicant -Dnl80211 -iwlan0 -c/path/to/wpa.conf -b br0

Signed-off-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>