With this patch, a new promiscuous mode is enabled. If the module is loaded
with the rtap_iface=1 module parameter, two interfaces will be created
(instead of just one).

The second interface is prefixed 'rtap' and provides received 802.11 frames
on the current channel to user space in a radiotap header format.

Example usage:

        % modprobe ipw2200 rtap_iface=1
        % iwconfig eth1 essid MyNetwork
        % dhcpcd eth1
        % tcpdump -i rtap0

If you do not specify 'rtap_iface=1' then the rtap interface will
not be created and you will need to turn it on via:

        % echo 1 > /sys/bus/pci/drivers/ipw2200/*/rtap_iface

You can filter out what type of information is passed to user space via
the rtap_filter sysfs entry.  Currently you can tell the driver to
transmit just the headers (which will provide the RADIOTAP and IEEE
802.11 header but not the payload), to filter based on frame control
type (Management, Control, or Data), and whether to report transmitted
frames, received frames, or both.

The transmit frame reporting is based on a patch by Stefan Rompf.

Filters can be get and set via a sysfs interface. For example, set the
filter to only send headers (0x7), don't report Tx'd frames (0x10), and
don't report data frames (0x100):

        % echo 0x117 > /sys/bus/pci/drivers/ipw2200/*/rtap_filter

All your packets are belong to us:

        % tethereal -n -i rtap0

Signed-off-by: James Ketrenos <jketreno@linux.intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>