staging: wfx: allow to send 802.11 frames

Three things make this task more complex than it should:
  - Chip necessitate to associate a link-id to each station. It is same
    thing than association ID but, using 8 bits only.
  - Rate policy is sent separately from Tx frames
  - Driver try to handle itself power saving of stations and multicast
    data

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20190919142527.31797-17-Jerome.Pouiller@silabs.com


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