[openthread] Update platform config file

Update max MLE children pre request from Nest team.

Update rx frame buffer to 24k to reduce the chance of having the rx
buffer full issue.

Added the header guard.

Change-Id: I1074d729326a8b500c6b2e61bd2a2a2390ffe23b
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/openthread/+/705165
Reviewed-by: Robert Quattlebaum <rquattle@google.com>
diff --git a/include/openthread-config-fuchsia.h b/include/openthread-config-fuchsia.h
index 993ab0d..0925ef9 100644
--- a/include/openthread-config-fuchsia.h
+++ b/include/openthread-config-fuchsia.h
@@ -26,6 +26,9 @@
  *  POSSIBILITY OF SUCH DAMAGE.
  */
 
+#ifndef THIRD_PARTY_OPENTHREAD_INCLUDE_OPENTHREAD_CONFIG_FUCHSIA_H_
+#define THIRD_PARTY_OPENTHREAD_INCLUDE_OPENTHREAD_CONFIG_FUCHSIA_H_
+
 #ifdef OPENTHREAD_CONFIG_ANDROID_VERSION_HEADER_ENABLE
 #include <openthread-config-android-version.h>
 #endif
@@ -172,4 +175,14 @@
  * The maximum number of children.
  *
  */
-#define OPENTHREAD_CONFIG_MLE_MAX_CHILDREN 64
+#define OPENTHREAD_CONFIG_MLE_MAX_CHILDREN 128
+
+/**
+ * @def OPENTHREAD_CONFIG_PLATFORM_RADIO_SPINEL_RX_FRAME_BUFFER_SIZE
+ *
+ * Rx frame buffer in openthread
+ *
+ */
+#define OPENTHREAD_CONFIG_PLATFORM_RADIO_SPINEL_RX_FRAME_BUFFER_SIZE 24576
+
+#endif // THIRD_PARTY_OPENTHREAD_INCLUDE_OPENTHREAD_CONFIG_FUCHSIA_H_