Avoids breakage of inline checks during test step.

DBUS option was added to wpa_supplicant and doesn't look
very useful.  Try to get away with switching it off globally
in order to avoid further ports from using such an option.

Makes 20.7 the default again (currently 5.7) while we remove
the long-term path from our ports that did this previously.

Build from 19.7.10 tag if necessary.