Moved ASYNCHRONOUS_DNS_SIMULTANEOUS_REPEAT under mbed extended tests

Test is giving problems in some networks. Could be that DNS server
is regarding repeated DNS enquiries on the test to be caused by
malfunctioning device.

TESTS/netsocket/dns/main.cpp

@@ -142,7 +142,9 @@ Case cases[] = {
     Case("ASYNCHRONOUS_DNS_EXTERNAL_EVENT_QUEUE", ASYNCHRONOUS_DNS_EXTERNAL_EVENT_QUEUE),
     Case("ASYNCHRONOUS_DNS_INVALID_HOST", ASYNCHRONOUS_DNS_INVALID_HOST),
     Case("ASYNCHRONOUS_DNS_TIMEOUTS", ASYNCHRONOUS_DNS_TIMEOUTS),
+#ifdef MBED_EXTENDED_TESTS
     Case("ASYNCHRONOUS_DNS_SIMULTANEOUS_REPEAT",  ASYNCHRONOUS_DNS_SIMULTANEOUS_REPEAT),
+#endif
 };
 
 Specification specification(test_setup, cases);