wil6210: add HW write-back option in TX descriptor

Map BIT 9 in TX DMA DWARD 0 as HW write back option.
We must turn on this option in the last TX descriptor,
this is required for old HW compatability.
This option indicate to HW that WB is required for this descriptor.

Signed-off-by: Kirshenbaum Erez <erezk@wilocity.com>
Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Git-commit: 668b2bbd7fd5a87e54e83b621658d4290811c4a0
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Liron Kuch <lkuch@codeaurora.org>