[805] updated the comments for listenAddresses() so that they match

what the function actually does.  The previous one was incorrect and just
confusing.

src/lib/testutils/portconfig.h

@@ -46,7 +46,7 @@ template<class Server>
 void
 listenAddresses(Server& server) {
     using namespace isc::server_common::portconfig;
-    // Default value should be fully recursive
+    // In this test we assume the address list is originally empty.
     EXPECT_TRUE(server.getListenAddresses().empty());
 
     // Try putting there some addresses
@@ -61,7 +61,8 @@ listenAddresses(Server& server) {
     addresses.clear();
     EXPECT_EQ(2, server.getListenAddresses().size());
 
-    // Did it return to fully recursive?
+    // If we set to an empty list next, the server configuration should
+    // become empty, too.
     server.setListenAddresses(addresses);
     EXPECT_TRUE(server.getListenAddresses().empty());
 }