MINOR: stats: prepare to add a description with each stat/info field

Several times some users have expressed the non-intuitive aspect of some
of our stat/info metrics and suggested to add some help. This patch
replaces the char* arrays with an array of name_desc so that we now have
some reserved room to store a description with each stat or info field.
These descriptions are currently empty and not reported yet.
diff --git a/include/proto/stats.h b/include/proto/stats.h
index 6144d2f..d20beea 100644
--- a/include/proto/stats.h
+++ b/include/proto/stats.h
@@ -92,12 +92,11 @@
 
 extern const char *stat_status_codes[];
 
-/* These two structs contains all field names according with
- * the the number of entries in "enum stat_field" and
- * "enum info_field"
+/* These two structs contains all field names and descriptions according to
+ * the the number of entries in "enum stat_field" and "enum info_field"
  */
-extern const char *info_field_names[];
-extern const char *stat_field_names[];
+extern const struct name_desc stat_fields[];
+extern const struct name_desc info_fields[];
 
 int stats_fill_info(struct field *info, int len);
 int stats_fill_fe_stats(struct proxy *px, struct field *stats, int len);