iwlcore: Set rb_timeout to 0x10 for devices with ICT

rb value should be 0x10 for devices using ICT.
 RX interrupt was not performing well with
 0 value

Signed-off-by: Mohamed Abbas <mohamed.abbas@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>