nios2: dts: Fix tse_mac "max-frame-size" property

The given value of 1518 seems to refer to the layer 2 ethernet frame
size without 802.1Q tag. Actual use of the "max-frame-size" including in
the consumer of the "altr,tse-1.0" compatible is the MTU.

Fixes: 95acd4c7b69c ("nios2: Device tree support")
Fixes: 61c610ec61bb ("nios2: Add Max10 device tree")
Cc: <[e-mail]>
Signed-off-by: Janne Grunau <[e-mail]>
Signed-off-by: Dinh Nguyen <[e-mail]>

arch/nios2/boot/dts/10m50_devboard.dts

···
 			rx-fifo-depth = <8192>;
 			tx-fifo-depth = <8192>;
 			address-bits = <48>;
-			max-frame-size = <1518>;
+			max-frame-size = <1500>;
 			local-mac-address = [00 00 00 00 00 00];
 			altr,has-supplementary-unicast;
 			altr,enable-sup-addr = <1>;

arch/nios2/boot/dts/3c120_devboard.dts

···
 				interrupt-names = "rx_irq", "tx_irq";
 				rx-fifo-depth = <8192>;
 				tx-fifo-depth = <8192>;
-				max-frame-size = <1518>;
+				max-frame-size = <1500>;
 				local-mac-address = [ 00 00 00 00 00 00 ];
 				phy-mode = "rgmii-id";
 				phy-handle = <&phy0>;