[simulation] enhance simulation for OTNS (#4268)

This commit is to support OTNS by:
- raising the max number of simulating nodes to 999 if OTNS=1
- implementing the status-push mechanism

To build:

$ make -f examples/Makefile-simulation OTNS=1

This commit should have no change of OpenThread behaviors on platforms
except simulation.

include/openthread/instance.h

@@ -149,6 +149,7 @@ enum
     OT_CHANGED_THREAD_NETIF_STATE           = 1 << 24, ///< Thread network interface state changed
     OT_CHANGED_THREAD_BACKBONE_ROUTER_STATE = 1 << 25, ///< Backbone Router state changed
     OT_CHANGED_THREAD_BACKBONE_ROUTER_LOCAL = 1 << 26, ///< Local Backbone Router configuration changed
+    OT_CHANGED_JOINER_STATE                 = 1 << 27, ///< Joiner state changed
 };
 
 /**

include/openthread/platform/Makefile.am

@@ -38,6 +38,7 @@ ot_platform_headers                     = \
     memory.h                              \
     misc.h                                \
     logging.h                             \
+    otns.h                                \
     radio.h                               \
     time.h                                \
     uart.h                                \

include/openthread/platform/otns.h

@@ -0,0 +1,83 @@
+/*
+ *  Copyright (c) 2019, The OpenThread Authors.
+ *  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 of the copyright holder 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 HOLDER 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
+ * @brief
+ *   This file includes the abstraction for the platform OTNS utilities.
+ *
+ *   OTNS is an OpenThread Network Simulator that simulates Thread networks using OpenThread simulation instances and
+ *   provides visualization and management of those simulated networks.
+ *   Refer to https://github.com/openthread/ot-ns for more information about OTNS.
+ */
+
+#ifndef OPENTHREAD_PLATFORM_OTNS_H_
+#define OPENTHREAD_PLATFORM_OTNS_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @addtogroup plat-otns
+ *
+ * @brief
+ *   This module includes the platform abstraction for OTNS.
+ *
+ * @{
+ *
+ */
+
+/**
+ * This function exports status information to OTNS.
+ *
+ * The status information is represented by a null-terminated string with format recognizable by OTNS.
+ * Each call to `otPlatOtnsStatus` can send multiple statuses, separated by ';', e.x. "parid=577fbc37;lrid=5".
+ * Each status contains key and value separated by '='.
+ * Status value can be further separated into multiple fields using ',',
+ * e.x. "ping_request=fdde:ad00:beef:0:459e:d7b4:b65e:5480,4,112000".
+ *
+ * New statuses should follow these conventions.
+ *
+ * Currently, OTNS only supports virtual time simulation.
+ *
+ * @param[in]  aStatus  The status string.
+ *
+ */
+void otPlatOtnsStatus(const char *aStatus);
+
+/**
+ * @}
+ *
+ */
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
+#endif // OPENTHREAD_PLATFORM_OTNS_H_