[netpfga] remove icmp support

No payload checksumming...

p4src/minip4_solution.p4

@@ -132,10 +132,7 @@ control RealMain(
                 exit;                      /* no further v6 processing */
 
             } else if(hdr.ipv4.isValid()) {
-                if(icmp.apply().hit) {
-                    v4_networks.apply();
-                    exit;
-                } else if(nat46.apply().hit) {
+                if(nat46.apply().hit) {
                     if(hdr.icmp.isValid()) {
                         nat46_icmp_generic();