[PATCH] softmac: suggest per-frame-type TX rate

This patch is the first step towards rate control inside softmac.

The txrates substructure has been extended to provide
different fields for different types of packets (management/data,
unicast/multicast). These fields are updated on association to values
compatible with the access point we are associating to.

Drivers can then use the new ieee80211softmac_suggest_txrate() function
call when deciding which rate to transmit each frame at. This is
immensely useful for ZD1211, and bcm can use it too.

The user can still specify a rate through iwconfig, which is matched
for all transmissions (assuming the rate they have specified is in
the rate set required by the AP).

At a later date, we can incorporate automatic rate management into
the ieee80211softmac_recalc_txrates() function.

This patch also removes the mcast_fallback field. Sam Leffler pointed
out that this field is meaningless, because no driver will ever be
retransmitting mcast frames (they are not acked).

Signed-off-by: Daniel Drake <dsd@gentoo.org>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>