Add new capabilities CAP_FREQ_2GHZ and CAP_FREQ_5GHZ to indicate the
frequency bands supported by a Wifi device.
Add also CAP_FREQ_VALID, which is set when the values of the other 2
capabilities are available.
Original patch by Dan Williams <dcbw@redhat.com>
https://bugzilla.gnome.org/show_bug.cgi?id=723295