WPS support in NM (client mode)

Simple push-button (PBC) support

The most simple is push-button support, it could look like this:

The AP name is obtained from the WPS scan results (see new versions of iw for how to parse this).

Then once the button on the AP is pushed, wpa_supplicant sends an event WPS-AP-AVAILABLE-PBC. At that point, the scan results are checked (akin wpa_cli scan_results) whether the selected BSS contains WPS-PBC, like this:

00:1d:7e:4a:a1:ab       2432    69      [WPA2-PSK-TKIP+CCMP][WPS-PBC]   jo

If it does, the button "Connect with WPS" becomes available. When pressed, we do the equivalent of wpa_cli wps_pbc 00:1d:7e:4a:a1:ab and wpa_supplicant does the rest, finally connecting to the network. We then obtain the network key from wpa_supplicant's network config stanza and save it.