Revert "mac80211: allow disable power save in mesh"

This reverts commit ee1f6681.

The aformentioned commit added a check to allow
'iw wlan0 set power_save off' to work for mesh interfaces.

However, this is problematic because it also allows
'iw wlan0 set power_save on', which will crash in short order
because all of the subsequent code manipulates sdata->u.mgd.

The power-saving states for mesh interfaces can be manipulated
through the mesh config, e.g:
'iw wlan0 set mesh_param mesh_power_save=active' (which,
despite the name, actualy disables power saving since the
setting refers to the type of sleep the interface undergoes).

Cc: stable@vger.kernel.org
Fixes: ee1f6681 ("mac80211: allow disable power save in mesh")
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>