mac80211: adjustable number of bits for qdisc pool

This fix allows to control the number of bits that qdiscs book keeping
can be done for with respect to the qdisc pool

Signed-off-by: Ron Rindjunsky <ron.rindjunsky@intel.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>