sfc: Firmware-Assisted TSO version 2

Add support for FATSOv2 to the driver. FATSOv2 offloads far more of the task
 of TCP segmentation to the firmware, such that we now just pass a single
 super-packet to the NIC. This means TSO has a great deal in common with a
 normal DMA transmit, apart from adding a couple of option descriptors.
 NIC-specific checks have been moved off the fast path and in to
 initialisation where possible.

This also moves FATSOv1/SWTSO to a new file (tx_tso.c).  The end of transmit
 and some error handling is now outside TSO, since it is common with other
 code.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sfc/nic.h

@@ -681,6 +681,8 @@ void efx_farch_tx_init(struct efx_tx_queue *tx_queue);
 void efx_farch_tx_fini(struct efx_tx_queue *tx_queue);
 void efx_farch_tx_remove(struct efx_tx_queue *tx_queue);
 void efx_farch_tx_write(struct efx_tx_queue *tx_queue);
+unsigned int efx_farch_tx_limit_len(struct efx_tx_queue *tx_queue,
+				    dma_addr_t dma_addr, unsigned int len);
 int efx_farch_rx_probe(struct efx_rx_queue *rx_queue);
 void efx_farch_rx_init(struct efx_rx_queue *rx_queue);
 void efx_farch_rx_fini(struct efx_rx_queue *rx_queue);