[mle] include Supervision TLV only from sleepy child (#10628)

This commit updates the code to include the Supervision Interval TLV
in MLE messages sent from a child only when the child mode indicates
it is sleepy (`!IsRxOnWhenIdle()`). The Network Diagnostic Child TLV
is also updated to use zero for the "Supervision Interval" field
when the child is not sleepy. The `test-023-mesh-diag.py` is updated
to validate this new behavior.

The parent node still tracks the received supervision interval from a
child in the `Child` entry. This parameter indicates the interval
that would be used if the child were to be supervised.

src/core/thread/mle.cpp

@@ -1776,7 +1776,7 @@ Error Mle::SendChildIdRequest(void)
     SuccessOrExit(error = message->AppendModeTlv(mDeviceMode));
     SuccessOrExit(error = message->AppendTimeoutTlv(mTimeout));
     SuccessOrExit(error = message->AppendVersionTlv());
-    SuccessOrExit(error = message->AppendSupervisionIntervalTlv(Get<SupervisionListener>().GetInterval()));
+    SuccessOrExit(error = message->AppendSupervisionIntervalTlvIfSleepyChild());
 
     if (!IsFullThreadDevice())
     {
@@ -2056,7 +2056,7 @@ Error Mle::SendChildUpdateRequest(ChildUpdateRequestMode aMode)
         SuccessOrExit(error = message->AppendSourceAddressTlv());
         SuccessOrExit(error = message->AppendLeaderDataTlv());
         SuccessOrExit(error = message->AppendTimeoutTlv((aMode == kAppendZeroTimeout) ? 0 : mTimeout));
-        SuccessOrExit(error = message->AppendSupervisionIntervalTlv(Get<SupervisionListener>().GetInterval()));
+        SuccessOrExit(error = message->AppendSupervisionIntervalTlvIfSleepyChild());
 #if OPENTHREAD_CONFIG_MAC_CSL_RECEIVER_ENABLE
         if (Get<Mac::Mac>().IsCslEnabled())
         {
@@ -2152,7 +2152,7 @@ Error Mle::SendChildUpdateResponse(const TlvList      &aTlvList,
             break;
 
         case Tlv::kSupervisionInterval:
-            SuccessOrExit(error = message->AppendSupervisionIntervalTlv(Get<SupervisionListener>().GetInterval()));
+            SuccessOrExit(error = message->AppendSupervisionIntervalTlvIfSleepyChild());
             break;
 
 #if OPENTHREAD_CONFIG_MAC_CSL_RECEIVER_ENABLE
@@ -4690,6 +4690,17 @@ exit:
     return error;
 }
 
+Error Mle::TxMessage::AppendSupervisionIntervalTlvIfSleepyChild(void)
+{
+    Error error = kErrorNone;
+
+    VerifyOrExit(!Get<Mle>().IsRxOnWhenIdle());
+    error = AppendSupervisionIntervalTlv(Get<SupervisionListener>().GetInterval());
+
+exit:
+    return error;
+}
+
 Error Mle::TxMessage::AppendSupervisionIntervalTlv(uint16_t aInterval)
 {
     return Tlv::Append<SupervisionIntervalTlv>(*this, aInterval);

src/core/thread/mle.hpp

@@ -1036,6 +1036,7 @@ private:
         Error AppendLinkMarginTlv(uint8_t aLinkMargin);
         Error AppendVersionTlv(void);
         Error AppendAddressRegistrationTlv(AddressRegistrationMode aMode = kAppendAllAddresses);
+        Error AppendSupervisionIntervalTlvIfSleepyChild(void);
         Error AppendSupervisionIntervalTlv(uint16_t aInterval);
         Error AppendXtalAccuracyTlv(void);
         Error AppendActiveTimestampTlv(void);

src/core/thread/network_diagnostic_tlvs.cpp

@@ -58,7 +58,7 @@ void ChildTlv::InitFrom(const Child &aChild)
     mTimeout             = BigEndian::HostSwap32(aChild.GetTimeout());
     mAge                 = BigEndian::HostSwap32(Time::MsecToSec(TimerMilli::GetNow() - aChild.GetLastHeard()));
     mConnectionTime      = BigEndian::HostSwap32(aChild.GetConnectionTime());
-    mSupervisionInterval = BigEndian::HostSwap16(aChild.GetSupervisionInterval());
+    mSupervisionInterval = aChild.IsRxOnWhenIdle() ? 0 : BigEndian::HostSwap16(aChild.GetSupervisionInterval());
     mLinkMargin          = aChild.GetLinkInfo().GetLinkMargin();
     mAverageRssi         = aChild.GetLinkInfo().GetAverageRss();
     mLastRssi            = aChild.GetLinkInfo().GetLastRss();

tests/toranj/cli/test-023-mesh-diag.py

@@ -136,9 +136,13 @@ r1.cli('meshdiag topology children')
 
 childtable = r2.cli('meshdiag childtable', r1_rloc)
 verify(len([line for line in childtable if line.startswith('rloc16')]) == 2)
+verify(len([line for line in childtable if ' supvn:0 ' in line]) == 1)
+verify(len([line for line in childtable if ' supvn:' in line and 'supvn:0' not in line]) == 1)
 
 childtable = r1.cli('meshdiag childtable', r3_rloc)
 verify(len([line for line in childtable if line.startswith('rloc16')]) == 3)
+verify(len([line for line in childtable if ' supvn:0 ' in line]) == 1)
+verify(len([line for line in childtable if ' supvn:' in line and 'supvn:0' not in line]) == 2)
 
 childtable = r1.cli('meshdiag childtable', r2_rloc)
 verify(len([line for line in childtable if line.startswith('rloc16')]) == 0)