Add wlvif->links_map bitmap to represent all the links
allocated for this vif.

AP vif also has a sta_hlid_map bitmap, which represents
the links stations connected to it (sta_hlid_bitmap is
a subset of wlvif->links_map, which itself is a subset
of the global wl->links_map)
Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>