[sub-mac] remove !OPENTHREAD_MTD check from CSL transmitter code (#13445)

This commit updates preprocessor guards controlling CSL transmitter code
in `SubMac` and `RadioSpinel` from:
`#if !OPENTHREAD_MTD && OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE`
to:
`#if OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE`

Throughout OpenThread core (such as `CslTxScheduler`, `IndirectSender`,
`DataPollHandler`, `MeshForwarder`, and `Mac`), CSL transmitter feature
logic is guarded solely by `OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE`
without excluding MTD builds via `!OPENTHREAD_MTD`. Updating `SubMac` and
`RadioSpinel` aligns them with this established pattern.

Additionally, this commit simplifies `MacLinks::Clear()` by removing
redundant preprocessor guards around reset of all TX frame properties
when clearing 802.15.4 frames.

src/core/mac/mac_links.hpp

@@ -171,15 +171,11 @@ public:
         mTxFrame802154.SetIsSecurityProcessed(false);
         mTxFrame802154.SetCsmaCaEnabled(true); // Set to true by default, only set to `false` for CSL transmission
         mTxFrame802154.SetIsHeaderUpdated(false);
-#if OPENTHREAD_FTD && OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
         mTxFrame802154.SetTxDelay(0);
         mTxFrame802154.SetTxDelayBaseTime(0);
-#endif
         mTxFrame802154.SetTxPower(Radio::kInvalidPower);
-#if OPENTHREAD_CONFIG_MAC_CSL_RECEIVER_ENABLE
         mTxFrame802154.SetCslIePresent(false);
 #endif
-#endif
 #if OPENTHREAD_CONFIG_RADIO_LINK_TREL_ENABLE
         mTxFrameTrel.SetLength(0);
         mTxFrameTrel.SetIsARetransmission(false);

src/core/mac/sub_mac.cpp

@@ -293,7 +293,7 @@ Error SubMac::Send(void)
     {
     case kStateDisabled:
     case kStateCsmaBackoff:
-#if !OPENTHREAD_MTD && OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
+#if OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
     case kStateCslTransmit:
 #endif
     case kStateTransmit:
@@ -390,7 +390,7 @@ exit:
 
 void SubMac::StartCsmaBackoff(void)
 {
-#if !OPENTHREAD_MTD && OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
+#if OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
     if (mTransmitFrame.GetTxDelay() != 0 || mTransmitFrame.GetTxDelayBaseTime() != 0)
     {
         SetState(kStateCslTransmit);
@@ -417,7 +417,7 @@ void SubMac::StartCsmaBackoff(void)
         BeginTransmit();
         ExitNow();
     }
-#endif // !OPENTHREAD_MTD && OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
+#endif // OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
 
     SetState(kStateCsmaBackoff);
 
@@ -466,7 +466,7 @@ void SubMac::BeginTransmit(void)
 {
     Error error;
 
-#if !OPENTHREAD_MTD && OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
+#if OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
     VerifyOrExit(mState == kStateCsmaBackoff || mState == kStateCslTransmit);
 #else
     VerifyOrExit(mState == kStateCsmaBackoff);
@@ -712,7 +712,7 @@ Error SubMac::EnergyScan(uint8_t aScanChannel, uint16_t aScanDuration)
     case kStateDisabled:
     case kStateCsmaBackoff:
     case kStateTransmit:
-#if !OPENTHREAD_MTD && OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
+#if OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
     case kStateCslTransmit:
 #endif
 #if OPENTHREAD_CONFIG_MAC_ADD_DELAY_ON_NO_ACK_ERROR_BEFORE_RETRY
@@ -794,7 +794,7 @@ void SubMac::HandleTimer(void)
 {
     switch (mState)
     {
-#if !OPENTHREAD_MTD && OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
+#if OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
     case kStateCslTransmit:
         BeginTransmit();
         break;
@@ -1084,7 +1084,7 @@ const char *SubMac::StateToString(State aState)
 #define DelayBeforeRetxStateMapList(_)
 #endif
 
-#if !OPENTHREAD_MTD && OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
+#if OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
 #define CslTxStateMapList(_) _(kStateCslTransmit, "CslTransmit")
 #else
 #define CslTxStateMapList(_)

src/core/mac/sub_mac.hpp

@@ -538,7 +538,7 @@ private:
 #if OPENTHREAD_CONFIG_MAC_ADD_DELAY_ON_NO_ACK_ERROR_BEFORE_RETRY
         kStateDelayBeforeRetx, // Delay before retx
 #endif
-#if !OPENTHREAD_MTD && OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
+#if OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
         kStateCslTransmit, // CSL transmission.
 #endif
 #if OPENTHREAD_CONFIG_MAC_CSL_RECEIVER_ENABLE || OPENTHREAD_CONFIG_WAKEUP_END_DEVICE_ENABLE

src/core/radio/radio_callbacks.cpp

@@ -60,7 +60,7 @@ void Callbacks::HandleEnergyScanDone(int8_t aMaxRssi) { Get<Mac::SubMac>().Handl
 
 void Callbacks::HandleBusLatencyChanged(void)
 {
-#if OPENTHREAD_FTD && OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
+#if OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE && (OPENTHREAD_FTD || OPENTHREAD_MTD)
     Get<CslTxScheduler>().HandleRadioBusLatencyChanged();
 #endif
 #if OPENTHREAD_FTD && OPENTHREAD_CONFIG_WAKEUP_COORDINATOR_ENABLE

src/lib/spinel/radio_spinel.cpp

@@ -1642,7 +1642,7 @@ otError RadioSpinel::Transmit(otRadioFrame &aFrame)
             uint32_t transmitDelay = 0;
 
             // If supported, add a delay and transmit the network time at a precise moment
-#if !OPENTHREAD_MTD && OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
+#if OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
             transmitDelay                                  = kTxWaitUs / 10;
             mTransmitFrame->mInfo.mTxInfo.mTxDelayBaseTime = static_cast<otRadioTime32>(netRadioTime);
             mTransmitFrame->mInfo.mTxInfo.mTxDelay         = transmitDelay;