mwl8k: implement AP firmware station database maintenance

STA firmware uses UPDATE_STADB to manipulate the hardware station
database, whereas AP firmware uses SET_NEW_STN -- this implements the
latter, and hooks it into mwl8k_sta_notify(), to be used if we're
running on AP firmware.

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