iwlwifi: add internal short scan support for 3945

Add internal short scan support for 3945 NIC, This allows 3945 NIC
to support radio reset request like the other series of NICs.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>