iwl3945: Use iwl-rfkill

Here again, the rfkill routines are duplicated between agn and 3945. Let's
move the agn one to iwlcore, and so we can get rid of the 3945 ones.

Signed-off-by: Samuel Ortiz <samuel.ortiz@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>