add license to rw_locking.h header

(cherry picked from commit e3a57ac)

rw_locking.h

@@ -1,3 +1,24 @@
+/*
+ * Copyright (C) 2016 OpenSIPS Project
+ *
+ * This file is part of opensips, a free SIP server.
+ *
+ * opensips is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version
+ *
+ * opensips is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301 USA
+ */
+
 #ifndef _rw_locking_h
 #define _rw_locking_h