wifi: cfg80211/mac80211: separate link params from station params

Put the link_station_parameters structure in the station_parameters
structure (and remove the station_parameters fields already existing
in link_station_parameters).
Now, for an MLD station, the default link is added together with
the station.

Signed-off-by: Shaul Triebitz <shaul.triebitz@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>