pg: allow creating pg for udp based protocols

f.g., gtpu4/6

Change-Id: I8bb1dc5fd2fba89ff17ec069a9816bafb9684190
Signed-off-by: Kingwel Xie <kingwel.xie@ericsson.com>
diff --git a/src/vnet/udp/udp.h b/src/vnet/udp/udp.h
index 91d063a..3b6de6c 100644
--- a/src/vnet/udp/udp.h
+++ b/src/vnet/udp/udp.h
@@ -107,6 +107,9 @@
 
   /* Next index for this type. */
   u32 next_index;
+
+  /* Parser for packet generator edits for this protocol */
+  unformat_function_t *unformat_pg_edit;
 } udp_dst_port_info_t;
 
 typedef enum