mac80211: pid, fix memory corruption

pid doesn't count with some band having more bitrates than the one
associated the first time.
Fix that by counting the maximal available bitrate count and allocate
big enough space.

Secondly, fix touching uninitialized memory which causes panics.
Index sucked from this random memory points to the hell.
The fix is to sort the rates on each band change.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>