ravb: add support for changing MTU

Allow for changing the MTU within the limit of the maximum size of a
descriptor (2048 bytes). Add the callback to change MTU from user-space
and take the configurable MTU into account when configuring the
hardware.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/renesas/ravb.h b/drivers/net/ethernet/renesas/ravb.h
index 96a27b0..b81f4fa 100644
--- a/drivers/net/ethernet/renesas/ravb.h
+++ b/drivers/net/ethernet/renesas/ravb.h
@@ -1018,6 +1018,7 @@
 	u32 dirty_rx[NUM_RX_QUEUE];	/* Producer ring indices */
 	u32 cur_tx[NUM_TX_QUEUE];
 	u32 dirty_tx[NUM_TX_QUEUE];
+	u32 rx_buf_sz;			/* Based on MTU+slack. */
 	struct napi_struct napi[NUM_RX_QUEUE];
 	struct work_struct work;
 	/* MII transceiver section. */