iwlwifi: add commit_rxon lib

Patch adds commit_rxon lib operation to iwlwifi and iwl3945 drivers.

Signed-off-by: Abhijeet Kolekar <abhijeet.kolekar@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>