mle class initialisation (ARMmbed#1488)

done with table size of one less than device description
table size, as the last entry in device description
table is reserved for for key id 2. This allows
discovery responses to be sent even when the
neighbour table is full.

Author: deepakvenugopal

source/6LoWPAN/Thread/thread_bootstrap.c

@@ -247,7 +247,7 @@ int8_t thread_mle_class_init(int8_t interface_id)
         return -1;
     }
 
-    if (mle_class_init(interface_id, buffer.device_decription_table_size, &thread_neighbor_remove, &thread_child_keep_alive, &thread_interface_is_active) != 0) {
+    if (mle_class_init(interface_id, buffer.device_decription_table_size - 1, &thread_neighbor_remove, &thread_child_keep_alive, &thread_interface_is_active) != 0) {
         return -1;
     }