[mpl] use TimeTicker for aging mSeedSet entries (#8488)

This commit updates the `Ip6::Mpl` to use `TimeTicker` instead of
its own `Timer` to age the entries in its `mSeedSet`. This commit
also updates the default number of seed entries by 3 to use the
memory saved by using `TimeTicker`.

src/core/common/time_ticker.cpp

@@ -124,6 +124,11 @@ void TimeTicker::HandleTimer(void)
         Get<MlrManager>().HandleTimeTick();
     }
 #endif
+
+    if (mReceivers & Mask(kIp6Mpl))
+    {
+        Get<Ip6::Mpl>().HandleTimeTick();
+    }
 }
 
 } // namespace ot

src/core/common/time_ticker.hpp

@@ -72,6 +72,7 @@ public:
         kDuaManager,             ///< `DuaManager`
         kMlrManager,             ///< `MlrManager`
         kNetworkDataNotifier,    ///< `NetworkData::Notifier`
+        kIp6Mpl,                 ///< `Ip6::Mpl`
 
         kNumReceivers, ///< Number of receivers.
     };

src/core/config/ip6.h

@@ -136,7 +136,7 @@
  *
  */
 #ifndef OPENTHREAD_CONFIG_MPL_SEED_SET_ENTRIES
-#define OPENTHREAD_CONFIG_MPL_SEED_SET_ENTRIES 32
+#define OPENTHREAD_CONFIG_MPL_SEED_SET_ENTRIES 35
 #endif
 
 /**

src/core/net/ip6_mpl.cpp

@@ -46,7 +46,6 @@ namespace Ip6 {
 
 Mpl::Mpl(Instance &aInstance)
     : InstanceLocator(aInstance)
-    , mSeedSetTimer(aInstance)
     , mSequence(0)
 #if OPENTHREAD_FTD
     , mRetransmissionTimer(aInstance)
@@ -252,19 +251,16 @@ Error Mpl::UpdateSeedSet(uint16_t aSeedId, uint8_t aSequence)
     insert->mSequence = aSequence;
     insert->mLifetime = kSeedEntryLifetime;
 
-    if (!mSeedSetTimer.IsRunning())
-    {
-        mSeedSetTimer.Start(kSeedEntryLifetimeDt);
-    }
+    Get<TimeTicker>().RegisterReceiver(TimeTicker::kIp6Mpl);
 
 exit:
     return error;
 }
 
-void Mpl::HandleSeedSetTimer(void)
+void Mpl::HandleTimeTick(void)
 {
-    bool startTimer = false;
-    int  j          = 0;
+    bool continueRxingTicks = false;
+    int  j                  = 0;
 
     for (int i = 0; i < kNumSeedEntries && mSeedSet[i].mLifetime; i++)
     {
@@ -272,8 +268,8 @@ void Mpl::HandleSeedSetTimer(void)
 
         if (mSeedSet[i].mLifetime > 0)
         {
-            mSeedSet[j++] = mSeedSet[i];
-            startTimer    = true;
+            mSeedSet[j++]      = mSeedSet[i];
+            continueRxingTicks = true;
         }
     }
 
@@ -282,9 +278,9 @@ void Mpl::HandleSeedSetTimer(void)
         mSeedSet[j].mLifetime = 0;
     }
 
-    if (startTimer)
+    if (!continueRxingTicks)
     {
-        mSeedSetTimer.Start(kSeedEntryLifetimeDt);
+        Get<TimeTicker>().UnregisterReceiver(TimeTicker::kIp6Mpl);
     }
 }
 

src/core/net/ip6_mpl.hpp

@@ -39,6 +39,7 @@
 #include "common/locator.hpp"
 #include "common/message.hpp"
 #include "common/non_copyable.hpp"
+#include "common/time_ticker.hpp"
 #include "common/timer.hpp"
 #include "net/ip6_headers.hpp"
 
@@ -185,6 +186,8 @@ private:
  */
 class Mpl : public InstanceLocator, private NonCopyable
 {
+    friend class ot::TimeTicker;
+
 public:
     /**
      * This constructor initializes the MPL object.
@@ -244,14 +247,11 @@ private:
         uint8_t  mLifetime;
     };
 
-    void  HandleSeedSetTimer(void);
+    void  HandleTimeTick(void);
     Error UpdateSeedSet(uint16_t aSeedId, uint8_t aSequence);
 
-    using SeedSetTimer = TimerMilliIn<Mpl, &Mpl::HandleSeedSetTimer>;
-
-    SeedEntry    mSeedSet[kNumSeedEntries];
-    SeedSetTimer mSeedSetTimer;
-    uint8_t      mSequence;
+    SeedEntry mSeedSet[kNumSeedEntries];
+    uint8_t   mSequence;
 
 #if OPENTHREAD_FTD
     static constexpr uint8_t kChildTimerExpirations  = 0; // MPL retransmissions for Children.