MINOR: arg: Add support for ARGT_PBUF_FNUM arg type.

This new argument type is used to parse Protocol Buffers field number
with dotted notation (e.g: 1.2.3.4).
diff --git a/include/types/arg.h b/include/types/arg.h
index 96974ba..6580c15 100644
--- a/include/types/arg.h
+++ b/include/types/arg.h
@@ -29,6 +29,7 @@
 #include <common/mini-clist.h>
 
 #include <types/vars.h>
+#include <types/protocol_buffers.h>
 
 /* encoding of each arg type : up to 31 types are supported */
 #define ARGT_BITS      5
@@ -60,6 +61,7 @@
 	ARGT_MAP,      /* a pointer to a map descriptor */
 	ARGT_REG,      /* a pointer to a regex */
 	ARGT_VAR,      /* contains a variable description. */
+	ARGT_PBUF_FNUM, /* a protocol buffer field number */
 	/* please update arg_type_names[] in args.c if you add entries here */
 };
 
@@ -100,6 +102,7 @@
 	struct userlist *usr;
 	struct map_descriptor *map;
 	struct my_regex *reg;
+	struct pbuf_fid fid;
 	struct var_desc var;
 };