mwl8k: pass in HT capabilities and rates when associating

Pass the AP's MCS rate mask to SET_RATE when associating, and make
UPDATE_STADB pass in the peer's HT caps and rates when adding a new
hardware station database entry.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>