wil6210: add scatter-gather support

When setting fragmented skb for Tx, assign skb to the last descriptor
and set number of fragments in the 1-st one
On Tx complete, HW sets "DU" bit in Tx descriptor only for the last
descriptor; so search for it using number of fragments field.
Middle descriptors may have "DU" bit not set by the hardware.

Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Git-commit: c236658f1434a1e00ec1fec9054964bcaf3ddde7
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


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