gnrc_netreg: optimize gnrc_netreg_num() to use _netreg_lookup()

sys/net/gnrc/netreg/gnrc_netreg.c

@@ -99,22 +99,11 @@ gnrc_netreg_entry_t *gnrc_netreg_lookup(gnrc_nettype_t type, uint32_t demux_ctx)
 int gnrc_netreg_num(gnrc_nettype_t type, uint32_t demux_ctx)
 {
     int num = 0;
-    gnrc_netreg_entry_t *entry;
+    gnrc_netreg_entry_t *entry = NULL;
 
-    if (_INVALID_TYPE(type)) {
-        return 0;
-    }
-
-    entry = netreg[type];
-
-    while (entry != NULL) {
-        if (entry->demux_ctx == demux_ctx) {
-            num++;
-        }
-
-        entry = entry->next;
+    while((entry = _netreg_lookup(entry, type, demux_ctx)) != NULL) {
+        num++;
     }
-
     return num;
 }