[mle] abort Address Solicit on partition change (#2481)

This commit aborts the Address Solicit transaction on a partition change.
Doing so avoids having Address Solicit messages being sent to the wrong
Leader address and delays caused by waiting for the previous Address Solicit
transaction to time out.

src/core/thread/mle.cpp

@@ -842,6 +842,7 @@ void Mle::SetLeaderData(uint32_t aPartitionId, uint8_t aWeighting, uint8_t aLead
 {
     if (mLeaderData.GetPartitionId() != aPartitionId)
     {
+        GetNetif().GetMle().HandlePartitionChange();
         mLastPartitionId = mLeaderData.GetPartitionId();
         mLastPartitionRouterIdSequence = GetNetif().GetMle().GetRouterIdSequence();
         mLastPartitionIdTimeout = GetNetif().GetMle().GetNetworkIdTimeout();

src/core/thread/mle_router.cpp

@@ -90,6 +90,14 @@ MleRouter::MleRouter(Instance &aInstance):
     SetRouterId(kInvalidRouterId);
 }
 
+void MleRouter::HandlePartitionChange(void)
+{
+    ThreadNetif &netif = GetNetif();
+
+    netif.GetAddressResolver().Clear();
+    netif.GetCoap().AbortTransaction(&MleRouter::HandleAddressSolicitResponse, this);
+}
+
 bool MleRouter::IsRouterRoleEnabled(void) const
 {
     return mRouterRoleEnabled && (mDeviceMode & ModeTlv::kModeFFD);
@@ -324,6 +332,7 @@ void MleRouter::StopLeader(void)
     mAdvertiseTimer.Stop();
     netif.GetNetworkDataLeader().Stop();
     netif.UnsubscribeAllRoutersMulticast();
+    HandlePartitionChange();
 }
 
 otError MleRouter::HandleDetachStart(void)

src/core/thread/mle_router_ftd.hpp

@@ -815,6 +815,8 @@ private:
 
     static bool IsSingleton(const RouteTlv &aRouteTlv);
 
+    void HandlePartitionChange(void);
+
     Child *NewChild(void);
     Child *FindChild(uint16_t aChildId);
     Child *FindChild(const Mac::ExtAddress &aMacAddr);

src/core/thread/mle_router_mtd.hpp

@@ -151,6 +151,7 @@ private:
     otError HandleDataRequest(const Message &, const Ip6::MessageInfo &) { return OT_ERROR_DROP; }
     otError HandleNetworkDataUpdateRouter(void) { return OT_ERROR_NONE; }
     otError HandleDiscoveryRequest(const Message &, const Ip6::MessageInfo &) { return OT_ERROR_DROP; }
+    void HandlePartitionChange(void) { }
 
     void StopAdvertiseTimer(void) { }
     otError ProcessRouteTlv(const RouteTlv &aRoute) { OT_UNUSED_VARIABLE(aRoute); return OT_ERROR_NONE; }