wil6210: Enable TCP/UDP checksum HW offload

Add support for TCP and UDP HW checksum offloading.
RX chain is allways configured for offload mode.
In case of checksum error in RX path the DMA L4 error bit(5)
will be set to 1 and driver will drop the packet.
TX checksum offloading is configrable (ethtool -K).
TX descriptors are configured for checksum offload according
to the SKB protocol type (TCP/UDP, IPV4/6), Upon mismatch drop
the TX packet (checksum required but not TCP/UDP IPV4/6 type).

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>