PRP on SoC4 models 6.4.3

Starting in 6.4.3, a PRP trailer header can be kept after passing through SoC4 model FortiGates in transparent mode.

To configure PRP:

1. Enable PRP:

   config system settings
       set prp-trailer-action enable
   end

2. Configure the PRP ports:

   config system npu
       set prp-port-in <ingress port>
       set prp-port-out <egress port>
   end

Testing results summary:

Model	Version and mode				Commands to enable PRP options
	6.2 TP	6.2 NAT	6.4 TP	6.4 NAT
SoC4	No	No	Pass	No	config system settings config system npu-setting prp
NP6	No	No	No	No	Not supported
NP7	Pass	No	-	-	config system settings
Non-NP platform	Pass	No	-	-	config system settings
VM64	Pass	No	Pass	No	config system settings