[indirect-sender] reset CSL Tx attempts in DataPollHandler (#8455)

Fix an issue in which a CSL Transmitter would start to send malformed
frames to the radio in the ocassion of a data poll arriving while a
delayed CSL transmission was already scheduled.

Notice that `CslTxScheduler::HandleSentFrame` is reseting both CSL Tx
attempts and Indirect Tx attempts, so it makes sense to do the same
in `DataPollHandler::HandleSentFrame`.

src/core/mac/data_poll_handler.cpp

@@ -240,6 +240,9 @@ void DataPollHandler::HandleSentFrame(const Mac::TxFrame &aFrame, Error aError,
     {
     case kErrorNone:
         aChild.ResetIndirectTxAttempts();
+#if OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
+        aChild.ResetCslTxAttempts();
+#endif
         aChild.SetFrameReplacePending(false);
         break;