fix(PRU-ICSS): Update cut thru documentation for switch mode

Cut thru documentation has a gap on the order of steps in which
the cut thru needs to be enabled. This commit fixes it by adding
the recommended steps order to follow for enabling cut thru.

Signed-off-by: Meghana Malladi <[email protected]>

Author: MeghanaMalladiTI

source/linux/Foundational_Components/PRU-ICSS/Linux_Drivers/PRU_ICSSG_Ethernet_Switch.rst

@@ -129,24 +129,18 @@ Assuming eth1 and eth2 are the active ports of ICSSG1 on AM64xx-EVM, to enable c
 
 .. code-block:: console
 
-   ip link set eth1 down
-   ip link set eth2 down
-
-   # To enable cut thru for slice0 q0
+   # To enable cut through for slice0 q0
    devlink dev param set platform/icssg1-eth name cut_thru value 1 cmode runtime
 
-   # To enable cut thru for slice0 q1
+   # To enable cut through for slice0 q1
    devlink dev param set platform/icssg1-eth name cut_thru value 2 cmode runtime
 
-   # To enable cut thru for slice0 q0, q1
+   # To enable cut through for slice0 q0, q1
    devlink dev param set platform/icssg1-eth name cut_thru value 3 cmode runtime
 
-   # To enable cut thru for slice0 q0, q1 and slice1 q0, q1
+   # To enable cut through for slice0 q0, q1 and slice1 q0, q1
    devlink dev param set platform/icssg1-eth name cut_thru value 771 cmode runtime
 
-   ip link set eth1 up
-   ip link set eth2 up
-
 To show the current cut through status, run the below command,
 
 .. code-block:: console
@@ -166,6 +160,13 @@ To disable cut through on all queues
 
    devlink dev param set platform/icssg1-eth name cut_thru value 0 cmode runtime
 
+.. note::
+
+    Set up the cut through value first before enabling switch mode to ensure that
+    cut through is working properly. This order ensures that firmware is loaded with the
+    expected cut through value. Setting up switch mode will automatically stop and start
+    the firmware so no need to bring links down and back up again.
+
 PTP
 """
 PTP can be run during switch mode. To run PTP in switch mode, 3 AM64x EVMs need to be connected with middle EVM acting as the switch. Use the following ptp config file on all slave EVMs. For Master EVM, priority1 filed needs to be changed.