Enable SYNCHRONOUS_DNS_CACHE just for NSAPI_PPP_AVAILABLE

Author: Ari Parkkila

TESTS/netsocket/dns/main.cpp

@@ -204,7 +204,9 @@ Case cases[] = {
     Case("ASYNCHRONOUS_DNS", ASYNCHRONOUS_DNS),
     Case("ASYNCHRONOUS_DNS_SIMULTANEOUS", ASYNCHRONOUS_DNS_SIMULTANEOUS),
     Case("ASYNCHRONOUS_DNS_SIMULTANEOUS_CACHE", ASYNCHRONOUS_DNS_SIMULTANEOUS_CACHE),
+#if NSAPI_PPP_AVAILABLE
     Case("SYNCHRONOUS_DNS_CACHE", SYNCHRONOUS_DNS_CACHE),
+#endif
 #ifndef MBED_CONF_CELLULAR_OFFLOAD_DNS_QUERIES
     Case("ASYNCHRONOUS_DNS_CACHE", ASYNCHRONOUS_DNS_CACHE),
 #endif