When a probe found no results, the list head of beacons would not be
freed, leaking 16 bytes of memory per probe.

Signed-off-by: Michael Brown <mcb30@etherboot.org>

Some cards (such as ath5k) always need to tune to a particular channel
when they are reset; the reset may happen upon open(), which is before
the channels array would be set up (in prepare_probe()). Avoid tuning
the card to an inconsistent state by copying the hardware
supported-channels array to the 802.11 device's allowable-channels
array even before channels are "properly" set up.

Signed-off-by: Michael Brown <mcb30@etherboot.org>

The prior net80211 model of physical-layer behavior for drivers was
overly simplistic and limited the drivers that could be written.  To
be more flexible, split the driver-provided list of supported rates by
band, and add a means for specifying a list of supported channels.
Allow drivers to specify a hardware channel value that will be tied to
uses of the channel.

Expose net80211_duration() to drivers, and make the rate it uses in
its computations configurable, so that it can be used in calculating
durations that must be set in hardware for ACK and CTS packets. Add
net80211_cts_duration() for the common case of calculating the
duration for a CTS packet.

Signed-off-by: Michael Brown <mcb30@etherboot.org>

This is required for all modern 802.11 devices, and allows drivers
to be written for them with minimally more effort than is required
for a wired NIC.

Signed-off-by: Michael Brown <mcb30@etherboot.org>
Modified-by: Michael Brown <mcb30@etherboot.org>