iwlwifi: simplify parameter setting to allow support for 6000 series

by parametrizing the set hw function, in addition to allowing for
supporting the 6000 family significantly simplify the addition of new
hardware.

Signed-off-by: Jay Sternberg <jay.e.sternberg@linux.intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>