iwlwifi: avoid commit rxon during scan in iwlagn_configure_filter

Almost anywhere in the code we avoid committing rxon while performing
scan, and make rxon commit when scan complete. However in some places
in the code we do not follow that rule. This patch fix that problem in
iwlagn_configure_filter().

Since we do not commit directly in iwl3945_configure_filter, we can
also do the same for agn, so I just remove iwlcore_commit_rxon()
function and add a comment. Also change comment for iwl3945.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>