HardwareVersion extended with UDID

dsdl/uavcan/protocol/HardwareVersion.uavcan

@@ -1,7 +1,12 @@
 #
 # Nested type.
 # Generic hardware version information.
+# These values should remain unchanged for the device's lifetime.
 #
 
 uint8 major
 uint8 minor
+
+# All zeros is not a valid UID.
+# If filled with zeros, assume that the value is undefined.
+uint8[16] unique_id

libuavcan/test/dsdl_test/dsdl_uavcan_compilability.cpp

@@ -59,6 +59,7 @@ TEST(Dsdl, Streaming)
         "hardware_version: \n"
         "  major: 0\n"
         "  minor: 0\n"
+        "  unique_id: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]\n"
         "software_version: \n"
         "  major: 0\n"
         "  minor: 0\n"