[settings] initialize structure before reading from storage (#4499)

This commit initializes	the settings structures	before reading.	This
helps prepare for a following commit that allows reading stored	values
that are shorter than expected.

This commit also renames the Clear() methods to Init().

src/core/common/settings.cpp

@@ -143,6 +143,7 @@ otError Settings::ReadNetworkInfo(NetworkInfo &aNetworkInfo) const
 {
     otError error;
 
+    aNetworkInfo.Init();
     SuccessOrExit(error = ReadFixedSize(kKeyNetworkInfo, &aNetworkInfo, sizeof(NetworkInfo)));
     LogNetworkInfo("Read", aNetworkInfo);
 
@@ -186,6 +187,7 @@ otError Settings::ReadParentInfo(ParentInfo &aParentInfo) const
 {
     otError error;
 
+    aParentInfo.Init();
     SuccessOrExit(error = ReadFixedSize(kKeyParentInfo, &aParentInfo, sizeof(ParentInfo)));
     LogParentInfo("Read", aParentInfo);
 
@@ -291,6 +293,7 @@ void Settings::ChildInfoIterator::Read(void)
     uint16_t size = sizeof(ChildInfo);
     otError  error;
 
+    mChildInfo.Init();
     SuccessOrExit(error = otPlatSettingsGet(&GetInstance(), kKeyChildInfo, mIndex,
                                             reinterpret_cast<uint8_t *>(&mChildInfo), &size));
     VerifyOrExit(size >= sizeof(ChildInfo), error = OT_ERROR_NOT_FOUND);

src/core/common/settings.hpp

@@ -92,7 +92,7 @@ public:
          * This method clears the struct object (setting all the fields to zero).
          *
          */
-        void Clear(void) { memset(this, 0, sizeof(*this)); }
+        void Init(void) { memset(this, 0, sizeof(*this)); }
 
         /**
          * This method returns the Thread role.
@@ -271,7 +271,7 @@ public:
          * This method clears the struct object (setting all the fields to zero).
          *
          */
-        void Clear(void) { memset(this, 0, sizeof(*this)); }
+        void Init(void) { memset(this, 0, sizeof(*this)); }
 
         /**
          * This method returns the extended address.
@@ -305,7 +305,7 @@ public:
          * This method clears the struct object (setting all the fields to zero).
          *
          */
-        void Clear(void) { memset(this, 0, sizeof(*this)); }
+        void Init(void) { memset(this, 0, sizeof(*this)); }
 
         /**
          * This method returns the extended address.

src/core/thread/mle.cpp

@@ -446,7 +446,7 @@ otError Mle::Store(void)
     otError               error = OT_ERROR_NONE;
     Settings::NetworkInfo networkInfo;
 
-    networkInfo.Clear();
+    networkInfo.Init();
 
     if (IsAttached())
     {
@@ -464,7 +464,7 @@ otError Mle::Store(void)
         {
             Settings::ParentInfo parentInfo;
 
-            parentInfo.Clear();
+            parentInfo.Init();
             parentInfo.SetExtAddress(mParent.GetExtAddress());
 
             SuccessOrExit(error = Get<Settings>().SaveParentInfo(parentInfo));

src/core/thread/mle_router.cpp

@@ -3617,7 +3617,7 @@ otError MleRouter::StoreChild(const Child &aChild)
 
     IgnoreReturnValue(RemoveStoredChild(aChild.GetRloc16()));
 
-    childInfo.Clear();
+    childInfo.Init();
     childInfo.SetExtAddress(aChild.GetExtAddress());
     childInfo.SetTimeout(aChild.GetTimeout());
     childInfo.SetRloc16(aChild.GetRloc16());