sfc: Move TX queue core queue mapping into tx.c

efx_hard_start_xmit() needs to implement a mapping which is the
inverse of tx_queue::core_txq.  Move the initialisation of
tx_queue::core_txq next to efx_hard_start_xmit() to make the
connection more obvious.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
diff --git a/drivers/net/sfc/efx.h b/drivers/net/sfc/efx.h
index d43a7e5..1162070 100644
--- a/drivers/net/sfc/efx.h
+++ b/drivers/net/sfc/efx.h
@@ -29,6 +29,7 @@
 extern int efx_probe_tx_queue(struct efx_tx_queue *tx_queue);
 extern void efx_remove_tx_queue(struct efx_tx_queue *tx_queue);
 extern void efx_init_tx_queue(struct efx_tx_queue *tx_queue);
+extern void efx_init_tx_queue_core_txq(struct efx_tx_queue *tx_queue);
 extern void efx_fini_tx_queue(struct efx_tx_queue *tx_queue);
 extern void efx_release_tx_buffers(struct efx_tx_queue *tx_queue);
 extern netdev_tx_t