wl12xx: AP-mode - configure STA HT rates on join

When a new STA joins the BSS, configure the HT rates it supports to the
FW.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>