mvebu: dts: enable IP checksum with jumbo frames for Armada 38x on Port0

The Ethernet controller found in the Armada 38x SoC's family support
TCP/IP checksumming with frame sizes larger than 1600 bytes, however
only on port 0.

This commit enables it by setting 'tx-csum-limit' to 9800B in
'ethernet@70000' node.
Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/arm/boot/dts/armada-38x.dtsi

@@ -498,6 +498,7 @@ eth0: ethernet@70000 {
 				reg = <0x70000 0x4000>;
 				interrupts-extended = <&mpic 8>;
 				clocks = <&gateclk 4>;
+				tx-csum-limit = <9800>;
 				status = "disabled";
 			};