wlcore/wl18xx: Add functionality to accept TX rate per link

FW will provide a TX rate per link for each FW status,
and wlcore will be able to store the information for
the use of the mesh hwmp module.

This is used mainly in mesh.
Rates are reported when a mesh interface is up.

Signed-off-by: Maxim Altshul <maxim.altshul@ti.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>