wlcore: start sta role on CHANGED_BSSID

Make the connection flow simpler by starting
sta role on bssid change.

Currently, we start dev role when going idle-off,
and start the sta role only after association
indication. This complicates the connection
flow with some possible intermediate states.

Make it simpler by starting sta role on bssid change,
which now happens *before* auth req get sent.

Update the handling of mac80211's notifications
and change wl1271_join/unjoin accordingly -
* Split wl1271_join() into wlcore_join (tuning on
  a channel/bssid) and wlcore_set_assoc (configure
  sta after association).
* Rename wl1271_unjoin() to wlcore_unset_assoc(), as
  it is no longer the inversion of wl1271_join()
  (now it's only used to disconnect associated sta /
  joined ibss, without stopping the role).
* Set ssid before starting station role (needed for
  start_role(sta)

While on it, split wl1271_bss_info_changed_sta() into
some sub-functions.

since we no longer use dev role in the connection flow,
we now always use the hlid of the sta role.

Signed-off-by: Eliad Peller <eliad@wizery.com>
Reviewed-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>