wpa_supplicant: Add get_capability freq

wpa_supplicant: Add get_capability freq

Add "get_capability freq" command to print a more verbose list of
channels and frequencies in MHz. The tag "NO_IBSS" is added, if IBSS
mode is not allowed on a channel. This allows userspace programs to get
the frequencies and limitations associated with each channel.

This extends the information already provided in "get_capability
channels" but a new interface is chosen because of backwards
compatibility considerations.

Signed-hostap: Bruno Randolf <br1@einfach.org>