add osmo_stat_item_get_group_by_name_idxname()

Add "missing" API for looking up a stat_item_group by its index-name.
A subsequent patch, which adds stat_items to the CTRL interface, will
use this to look up stat item groups by object name.

In stat item groups, there are group names, having a number of indexes
denoting different objects. An object can have, besides the index, also
a name that is equivalent to the index.

Apologies for the weird function name, it's still the best one I
could come up with: "group_by_name" refers to the group name, and
"idxname" refers to the name that the object index is associated with.

We already have osmo_stat_item_get_group_by_name_idx().
Other contestants for name of this new function were:

- osmo_stat_item_get_group_by_name_name()
  because there is a "name" instead of "idx", but I find it confusing.

- osmo_stat_item_get_group_by_name_idx_name()
  but I find that the last "name" should be closer to the "idx".

Related: SYS#5542
Change-Id: Ia1a77a1e4657ba624dd4f4bf7ad274e7751d0141

include/osmocom/core/stat_item.h

@@ -97,6 +97,7 @@ int osmo_stat_item_init(void *tall_ctx);
 
 struct osmo_stat_item_group *osmo_stat_item_get_group_by_name_idx(
 	const char *name, const unsigned int idx);
+struct osmo_stat_item_group *osmo_stat_item_get_group_by_name_idxname(const char *group_name, const char *idx_name);
 
 const struct osmo_stat_item *osmo_stat_item_get_by_name(
 	const struct osmo_stat_item_group *statg, const char *name);

src/stat_item.c

@@ -333,6 +333,26 @@ struct osmo_stat_item_group *osmo_stat_item_get_group_by_name_idx(
 	return NULL;
 }
 
+/*! Search for item group based on group name and index's name.
+ *  \param[in] name Name of stats_item_group we want to find.
+ *  \param[in] idx_name Index of the group we want to find, by the index's name (osmo_stat_item_group->name).
+ *  \returns pointer to group, if found; NULL otherwise. */
+struct osmo_stat_item_group *osmo_stat_item_get_group_by_name_idxname(const char *group_name, const char *idx_name)
+{
+	struct osmo_stat_item_group *statg;
+
+	llist_for_each_entry(statg, &osmo_stat_item_groups, list) {
+		if (!statg->desc || !statg->name)
+			continue;
+		if (strcmp(statg->desc->group_name_prefix, group_name))
+			continue;
+		if (strcmp(statg->name, idx_name))
+			continue;
+		return statg;
+	}
+	return NULL;
+}
+
 /*! Search for item based on group + item name
  *  \param[in] statg group in which to search for the item
  *  \param[in] name name of item to search within \a statg