Changed the app-config-file option to be additive instead of comprehensive

Author: dreemkiller

features/mbedtls/inc/mbedtls/mbedtls_config_reader.h

@@ -27,7 +27,7 @@
 #include <limits.h>
 #include MBED_CONF_MBEDTLS_APP_CONFIG_FILE
 
-#else // MBED_CONF_MBEDTLS_APP_CONFIG_FILE
+#endif // else MBED_CONF_MBEDTLS_APP_CONFIG_FILE
 
 #if MBED_CONF_MBEDTLS_PELION_CLIENT
     #undef MBED_CONF_MBEDTLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256