support of multi uav simulation in SITL

src/modules/simulator/simulator_mavlink.cpp

@@ -619,7 +619,9 @@ void Simulator::pollForMAVLinkMessages(bool publish, int udp_port)
 	struct sockaddr_in _myaddr;
 
 	if (udp_port < 1) {
-		udp_port = UDP_PORT;
+		int prt;
+		param_get(param_find("SITL_UDP_PRT"), &prt);
+		udp_port = prt;
 	}
 
 	// try to setup udp socket for communcation with simulator

src/modules/simulator/simulator_params.c

@@ -0,0 +1,48 @@
+/****************************************************************************
+ *
+ *   Copyright (c) 2013-2015 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * AS IS AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/**
+ * @file simulator_params.c
+ *
+ * Parameters of software in the loop
+ *
+ * @author Mohamed Abdelkader <mohamedashraf123@gmail.com>
+ */
+#include <systemlib/param/param.h>
+
+/**
+ * Simulator UDP port
+ *
+ * @group SITL
+ */
+PARAM_DEFINE_INT32(SITL_UDP_PRT, 14560);