[1603] cleanup: put labelsequence tests in an unnamed namespace.

src/lib/dns/tests/labelsequence_unittest.cc

@@ -19,6 +19,8 @@
 
 using namespace isc::dns;
 
+namespace {
+
 class LabelSequenceTest : public ::testing::Test {
 public:
     LabelSequenceTest() : n1("example.org"), n2("example.com"),
@@ -254,3 +256,5 @@ TEST_F(LabelSequenceTest, isAbsolute) {
     ls3.stripLeft(2);
     ASSERT_TRUE(ls3.isAbsolute());
 }
+
+}