cli: indicate missing radio hardware in "nmcli radio"

When no radio hardware is present in the system, "nmcli radio" currently displays:

  WIFI-HW  WIFI     WWAN-HW  WWAN
  enabled  enabled  enabled  enabled

which is misleading. Use the new RadioFlags property to display "missing" in the *-HW columns when there is no hardware for the given radio technology.

https://bugzilla.redhat.com/show_bug.cgi?id=1996918