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
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