rt2x00: trim skb_frame_desc to 32 bytes

Remove frame_type from skb_frame_desc and pass it
as argument to rt2x00debug_dump_frame().

Change data_len and desc_len to unsigned short
to save another 4 bytes in skb_frame_desc. Note that
this was the only location where the data_len and
desc_len was not yet treated as unsigned short.

This trim is required to help mac80211 with adding
the TX control and TX status informtation into the
skb->cb structure. When that happens, drivers will
have approximately 40 bytes left to use freely.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>