Some fixes for creating wpa_supplicant config

Some general fixes for bugs I noticed while looking into the wpa_supplicant config generator code.

The removal of NM_SUPPL_CAP_TYPE_PMF makes the code easier to understand and gets rid of those weird "supplicant supports PMF == supplicant support sha256 hmac" assumptions, I hope it's fine to assume the wpa_supplicant version is newer than September 2019.