statistics: use namespace prefix osmo_counter*

Summary of changes:

s/struct counter/struct osmo_counter/g
s/counter_inc/osmo_counter_inc/g
s/counter_get/osmo_counter_get/g
s/counter_reset/osmo_counter_reset/g
s/counter_alloc/osmo_counter_alloc/g
s/counter_free/osmo_counter_free/g
s/counters_for_each/osmo_counters_for_each/g
diff --git a/src/statistics.c b/src/statistics.c
index 83bb6ed..e28541b 100644
--- a/src/statistics.c
+++ b/src/statistics.c
@@ -30,9 +30,9 @@
 
 void *tall_ctr_ctx;
 
-struct counter *counter_alloc(const char *name)
+struct osmo_counter *osmo_counter_alloc(const char *name)
 {
-	struct counter *ctr = talloc_zero(tall_ctr_ctx, struct counter);
+	struct osmo_counter *ctr = talloc_zero(tall_ctr_ctx, struct osmo_counter);
 
 	if (!ctr)
 		return NULL;
@@ -43,15 +43,16 @@
 	return ctr;
 }
 
-void counter_free(struct counter *ctr)
+void osmo_counter_free(struct osmo_counter *ctr)
 {
 	llist_del(&ctr->list);
 	talloc_free(ctr);
 }
 
-int counters_for_each(int (*handle_counter)(struct counter *, void *), void *data)
+int osmo_counters_for_each(int (*handle_counter)(struct osmo_counter *, void *),
+			   void *data)
 {
-	struct counter *ctr;
+	struct osmo_counter *ctr;
 	int rc = 0;
 
 	llist_for_each_entry(ctr, &counters, list) {
@@ -63,9 +64,9 @@
 	return rc;
 }
 
-struct counter *counter_get_by_name(const char *name)
+struct osmo_counter *osmo_counter_get_by_name(const char *name)
 {
-	struct counter *ctr;
+	struct osmo_counter *ctr;
 
 	llist_for_each_entry(ctr, &counters, list) {
 		if (!strcmp(ctr->name, name))