tweak the "copy current AP's MAC to BSSID" function

- only use the network interface the connection is restricted to
- only use the currently connected AP if the AP's SSID is the same as the
SSID in the input field, otherwise search the environment for a network
with this SSID and use it's BSSID
- above also enables the use of this function if creating a wireless connection
from scratch, with no AP connected
(cherry picked from commit ba9af8b8b5fe41a718f1a0436b22075068dae360)