iwlwifi: disable powersave for 4965

There's a bug in 4965 powersave that appears to
be related to the way it keeps track of its data
during sleep, but we haven't found it yet. Due to
that, using powersave may spontaneously cause the
device to SYSASSERT when transitioning from sleep
to wake. Therefore, disable powersave for 4965,
until (if ever, unfortunately) we can identify
and fix the problem.

Cf. http://bugzilla.intellinuxwireless.org/show_bug.cgi?id=1982


which was closed, but now has re-appeared with
IDLE mode, which probably means we never really
fixed it.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>