iwlwifi: add comments to iwl*-base.c

Add comments to iwlXXXX-base.c
Signed-off-by: NCahill, Ben M <ben.m.cahill@intel.com>
Signed-off-by: NZhu Yi <yi.zhu@intel.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>