openthread rcp: set link metrics feature optional

components/openthread/private_include/openthread-core-esp32x-radio-config.h

@@ -207,6 +207,7 @@
 
 #define OPENTHREAD_RADIO 1
 
+#if CONFIG_OPENTHREAD_LINK_METRICS
 /**
  * @def OPENTHREAD_CONFIG_MLE_LINK_METRICS_SUBJECT_ENABLE
  *
@@ -216,3 +217,4 @@
 #ifndef OPENTHREAD_CONFIG_MLE_LINK_METRICS_SUBJECT_ENABLE
 #define OPENTHREAD_CONFIG_MLE_LINK_METRICS_SUBJECT_ENABLE 1
 #endif
+#endif //CONFIG_OPENTHREAD_LINK_METRICS