mxqd: Sort groups by priority

When active groups are (re-)loaded from the database, we sort them by
group priority. This implements group priority (mxqsub -P).

mxqd.c

@@ -2239,6 +2239,7 @@ int load_running_groups(struct mxq_server *server)
     free(grps);
 
     server_remove_orphaned_groups(server);
+    server_sort_groups_by_priority(server);
 
     return total;
 }