staging: wfx: do not use link_map_cache to track CAB

Since we do not track power save status of the stations anymore,
link_map_cache is now only used to track "Content After (DTIM) Beacon".
We prefer to rely on flags from tx_info. So we will be able to drop
link_map_cache.

Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200401110405.80282-15-Jerome.Pouiller@silabs.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>