This patch changes the iwlwifi driver to properly support
monitor interfaces after the filter flags change.

The patch is originally created by Johannes Berg for iwl4965. I fixed some
of the comments and created a similar patch for iwl3945.
Signed-off-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NZhu Yi <yi.zhu@intel.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>