staging: wfx: do not rely anymore on link_id to choose packet in queue

staging: wfx: do not rely anymore on link_id to choose packet in queue

link_id was expected to contain identifier of a station. It was also
used to mark frames that has to sent after dtim. We do not use the
further purpose. For the last purpose, we can directly check the flag
value in tx_info.

Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200401110405.80282-17-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>