[mac_frame] process the security of the wakeup frame

If the radio driver supports the `OT_RADIO_CAPS_TRANSMIT_SEC`, the
radio driver should process the security of the send frame. But the
current method `otMacFrameProcessTransmitSecurity()` doesn't process
the security of the wakeup frame. Which causes sent wakeup frame is not
encrypted.

This commit enables the method `otMacFrameProcessTransmitSecurity()`
to process the security of the wakeup frame.

examples/platforms/utils/mac_frame.cpp

@@ -224,6 +224,16 @@ bool otMacFrameIsKeyIdMode1(otRadioFrame *aFrame)
     return (error == OT_ERROR_NONE) ? (keyIdMode == Mac::Frame::kKeyIdMode1) : false;
 }
 
+bool otMacFrameIsKeyIdMode2(otRadioFrame *aFrame)
+{
+    uint8_t keyIdMode;
+    otError error;
+
+    error = static_cast<const Mac::Frame *>(aFrame)->GetKeyIdMode(keyIdMode);
+
+    return (error == OT_ERROR_NONE) ? (keyIdMode == Mac::Frame::kKeyIdMode2) : false;
+}
+
 uint8_t otMacFrameGetKeyId(otRadioFrame *aFrame)
 {
     uint8_t keyId = 0;
@@ -306,9 +316,15 @@ otError otMacFrameProcessTransmitSecurity(otRadioFrame *aFrame, otRadioContext *
     otMacKeyMaterial *key = nullptr;
     uint8_t           keyId;
     uint32_t          frameCounter;
+    bool              processKeyId;
+
+    processKeyId =
+#if OPENTHREAD_CONFIG_WAKEUP_END_DEVICE_ENABLE
+        otMacFrameIsKeyIdMode2(aFrame) ||
+#endif
+        otMacFrameIsKeyIdMode1(aFrame);
 
-    VerifyOrExit(otMacFrameIsSecurityEnabled(aFrame) && otMacFrameIsKeyIdMode1(aFrame) &&
-                 !aFrame->mInfo.mTxInfo.mIsSecurityProcessed);
+    VerifyOrExit(otMacFrameIsSecurityEnabled(aFrame) && processKeyId && !aFrame->mInfo.mTxInfo.mIsSecurityProcessed);
 
     if (otMacFrameIsAck(aFrame))
     {

examples/platforms/utils/mac_frame.h

@@ -259,6 +259,16 @@ bool otMacFrameIsSecurityEnabled(otRadioFrame *aFrame);
  */
 bool otMacFrameIsKeyIdMode1(otRadioFrame *aFrame);
 
+/**
+ * Tell if the key ID mode of @p aFrame is 2.
+ *
+ * @param[in]   aFrame          A pointer to the frame.
+ *
+ * @retval  true    The frame key ID mode is 2.
+ * @retval  false   The frame security is not enabled or key ID mode is not 2.
+ */
+bool otMacFrameIsKeyIdMode2(otRadioFrame *aFrame);
+
 /**
  * Get the key ID of @p aFrame.
  *