For nm 1.22: add bridge to wpa supplicant

BridgeIfname isn't being passed to wpa_supplicant when NetworkManager inits it, when the connection has a bridge, so here's MR that will do that.

It will take the latest .nmconnection that matches the ifname and get the master='s value. Then it will pass that value to nm-supplicant-manager object, then to nm-supplicant-interface object, where it will be sent via dbus to wpa_supplicant (well, at least that's how I understand it).

This code is only for nm-1.22.* (actually testted in 1.22.10 via Ubuntu 20.04), and will not work for the newer version, since newer code changed. I'm submitting this for nm-1.22 since I tested it in Ubuntu 20.04 and hopefully be picked up there.

I'm still trying to create another MR for master or 1.27.3.

Update: sorry, if forgot, this should partially fix #83 (closed).