sfc: Properly distinguish RX buffer and DMA lengths

Replace efx_nic::rx_buffer_len with efx_nic::rx_dma_len, the maximum
RX DMA length.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h
index f74411f..fc6770e 100644
--- a/drivers/net/ethernet/sfc/net_driver.h
+++ b/drivers/net/ethernet/sfc/net_driver.h
@@ -669,8 +669,7 @@
  * @n_channels: Number of channels in use
  * @n_rx_channels: Number of channels used for RX (= number of RX queues)
  * @n_tx_channels: Number of channels used for TX
- * @rx_buffer_len: RX buffer length, including start alignment but excluding
- *	any metadata
+ * @rx_dma_len: Current maximum RX DMA length
  * @rx_buffer_order: Order (log2) of number of pages for each RX buffer
  * @rx_hash_key: Toeplitz hash key for RSS
  * @rx_indir_table: Indirection table for RSS
@@ -786,7 +785,7 @@
 	unsigned rss_spread;
 	unsigned tx_channel_offset;
 	unsigned n_tx_channels;
-	unsigned int rx_buffer_len;
+	unsigned int rx_dma_len;
 	unsigned int rx_buffer_order;
 	u8 rx_hash_key[40];
 	u32 rx_indir_table[128];