[mac-frame] check rx frame security level in GenerateEnhAck() (#9315)

This commit updates the `Mac::TxFrame::GenerateEnhAck()` method to
check the security level of the received frame. If the security level
is not `kSecurityEncMic32`, it will return `kErrorParse`. This should
help prevent radio platform implementations from trying to perform tx
security on an invalid generated enhanced ack frame. Specifically, it
can help prevent radio platforms from calling `ProcessTxSecurity()`
on an enhanced ack frame with a security level of `kSecurityNone`
which can cause an assert in `AesCcm::Init()` due to the tag length
being zero.

src/core/mac/mac_frame.cpp

@@ -1362,6 +1362,8 @@ Error TxFrame::GenerateEnhAck(const RxFrame &aFrame, bool aIsFramePending, const
         SuccessOrExit(error = aFrame.GetSecurityControlField(securityControlField));
         SuccessOrExit(error = aFrame.GetKeyId(keyId));
 
+        VerifyOrExit((securityControlField & kSecLevelMask) == kSecurityEncMic32, error = kErrorParse);
+
         SetSecurityControlField(securityControlField);
         SetKeyId(keyId);
     }