Temporarily move SYNCHRONOUS_DNS_CACHE test to extended set until issues fixed with it

Author: Jarno Lamsa

TESTS/netsocket/dns/main.cpp

@@ -178,7 +178,9 @@ Case cases[] = {
 #endif
     Case("SYNCHRONOUS_DNS", SYNCHRONOUS_DNS),
     Case("SYNCHRONOUS_DNS_MULTIPLE", SYNCHRONOUS_DNS_MULTIPLE),
+#ifdef MBED_EXTENDED_TESTS
     Case("SYNCHRONOUS_DNS_CACHE", SYNCHRONOUS_DNS_CACHE),
+#endif
     Case("SYNCHRONOUS_DNS_INVALID", SYNCHRONOUS_DNS_INVALID),
 };