rate_ctr: Store the numeric index as part of 'rate_ctr_group'

include/osmocore/rate_ctr.h

@@ -49,6 +49,7 @@ struct rate_ctr_group {
 	struct llist_head list;
 	/* Pointer to the counter group class */
 	const struct rate_ctr_group_desc *desc;
+	unsigned int idx;
 	/* The name prefix generated from desc->group_prefix_fmt and index */
 	char *name_prefix;
 	/* Actual counter structures below */

src/rate_ctr.c

@@ -51,6 +51,7 @@ struct rate_ctr_group *rate_ctr_group_alloc(void *ctx,
 		return NULL;
 
 	group->desc = desc;
+	group->idx = idx;
 	/* Generate the Group prefix from the user-specified index */
 	group->name_prefix = talloc_size(group, strlen(desc->group_prefix_fmt) + 20);
 	sprintf(group->name_prefix, desc->group_prefix_fmt, idx);