[dua] allow MTD to handle ADDR_ERR.ntf messages (#7844)

An MTD interface should be able to handle Address Error Notifications
as per Thread Specification section 5.6.4.

tests/scripts/thread-cert/v1_2_test_dua_handle_address_error.py

@@ -77,6 +77,7 @@ class TestDomainUnicastAddress(thread_cert.TestCase):
         },
         MED: {
             'version': '1.2',
+            'is_mtd': True,
             'allowlist': [ROUTER],
             'mode': 'rn',
         },