[master] Fix for 3387, asiodns::IOFetch unit test failing

The unit test, IOFetchTest.TcpSendReceive65535, was failing
routinely on a NetBSD VM.  The VM was running so slowly that
this test was timing out.  Typically it takes less than
500ms. On this VM it was taking over 4.5s and then hitting
a safety valve timeout.  That timeout value was increased.

src/lib/asiodns/tests/io_fetch_unittest.cc

@@ -106,7 +106,7 @@ public:
         udp_fetch_(IOFetch::UDP, service_, question_, IOAddress(TEST_HOST),
             TEST_PORT, result_buff_, this, 100),
         tcp_fetch_(IOFetch::TCP, service_, question_, IOAddress(TEST_HOST),
-            TEST_PORT, result_buff_, this, (16 * SEND_INTERVAL)),
+            TEST_PORT, result_buff_, this, (24 * SEND_INTERVAL)),
                                         // Timeout interval chosen to ensure no timeout
         protocol_(IOFetch::TCP),        // for initialization - will be changed
         cumulative_(0),