Feature/mstp zero config option (#564)

* Added a MS/TP zero-config (automatically choose an unused MAC address) using an algorithm that starts with MAC=64 and waits for a random number of PFM (minimum of 8 plus modulo 64) before attempting to choose a MAC sequentially from 64..127. The confirmation uses a 128-bit UUID with the MSTP Test Request frame. The modifications are in src/bacnet/datalink/mstp.c and src/bacnet/datalink/dlmstp.c modules enabling any device to use zero-config if enabled. A working demonstration is in the ports/stm32f4xx for the NUCLEO board. Complete unit testing is included.  Options include lurking forever (wait for a router or another master node before joining) or lurking for a minimum time (enables self forming automatic MAC addressing device nodes).

ports/stm32f4xx/device.c

@@ -77,7 +77,7 @@ static struct my_object_functions {
    properties that are writable or that may change.
    The properties that are constant can be hard coded
    into the read-property encoding. */
-static uint32_t Object_Instance_Number = 103;
+static uint32_t Object_Instance_Number = BACNET_MAX_INSTANCE;
 static BACNET_DEVICE_STATUS System_Status = STATUS_OPERATIONAL;
 static BACNET_CHARACTER_STRING My_Object_Name;
 static const char *Device_Name_Default = "stm32f4xx";
@@ -1131,9 +1131,8 @@ void Device_Init(object_functions_t *object_table)
         pObject++;
     }
     dcc_set_status_duration(COMMUNICATION_ENABLE, 0);
-    if (Object_Instance_Number >= BACNET_MAX_INSTANCE) {
-        Object_Instance_Number = 103;
-        srand(Object_Instance_Number);
+    if (Object_Instance_Number > BACNET_MAX_INSTANCE) {
+        Object_Instance_Number = BACNET_MAX_INSTANCE;
     }
     characterstring_init_ansi(&My_Object_Name, Device_Name_Default);
 }